Modified G-CSF polypeptide

ABSTRACT

The present invention relates to granulocyte colony-stimulating factor (“G-CSF”) hybrid molecules which retain the internal core helices of G-CSF. Also provided are pharmaceutical compositions containing hybrid molecules.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10/032,108, filed Dec. 20, 2001, now U.S. Pat. No. 7,381,804, whichis a divisional of U.S. patent application Ser. No. 09/754,532, filedJan. 3, 2001, now U.S. Pat. No. 6,632,426, which is a divisional of U.S.patent application Ser. No. 09/304,186, filed May 3, 1999, now U.S. Pat.No. 6,261,550, which is a continuation of U.S. patent application Ser.No. 09/027,508, filed Feb. 20, 1998, now abandoned, which is acontinuation of U.S. patent application Ser. No. 08/956,812, filed Oct.23, 1997, now abandoned which is a divisional of U.S. patent applicationSer. No. 08/448,716, filed May 24, 1995, now U.S. Pat. No. 5,790,421,which is a divisional of U.S. patent application Ser. No. 08/010,099,filed Jan. 28, 1993, now U.S. Pat. No. 5,581,476, all of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to granulocyte colony stimulating factor(“G-CSF”) analogs, compositions containing such analogs, and relatedcompositions. In another aspect, the present invention relates tonucleic acids encoding the present analogs or related nucleic acids,related host cells and vectors. In another aspect, the invention relatesto computer programs and apparatuses for expressing the threedimensional structure of G-CSF and analogs thereof. In another aspect,the invention relates to methods for rationally designing G-CSF analogsand related compositions. In yet another aspect, the present inventionrelates to methods for treatment using the present G-CSF analogs.

2. Description of the Related Art

Hematopoiesis is controlled by two systems: the cells within the bonemarrow microenvironment and growth factors. The growth factors, alsocalled colony stimulating factors, stimulate committed progenitor cellsto proliferate and to form colonies of differentiating blood cells. Oneof these factors is granulocyte colony stimulating factor, herein calledG-CSF, which preferentially stimulates the growth and development ofneutrophils, indicating a potential use in neutropenic states. Welte etal. PNAS-USA 82: 1526-1530 (1985); Souza et al. Science 232: 61-65(1986) and Gabrilove, J. Seminars in Hematology 26:2 1-14 (1989).

In humans, endogenous G-CSF is detectable in blood plasma. Jones et al.Bailliere's Clinical Hematology 2:1 83-111 (1989). G-CSF is produced byfibroblasts, macrophages, T cells trophoblasts, endothelial cells andepithelial cells and is the expression product of a single copy genecomprised of four exons and five introns located on chromosomeseventeen. Transcription of this locus produces a mRNA species which isdifferentially processed, resulting in two forms of G-CSF mRNA, oneversion coding for a protein of 177 amino acids, the other coding for aprotein of 174 amino acids, Nagata et al. EMBO J 5: 575-581 (1986), andthe form comprised of 174 amino acids has been found to have thegreatest specific in vivo biological activity. G-CSF is speciescross-reactive, such that when human G-CSF is administered to anothermammal such as a mouse, canine or monkey, sustained neutrophilleukocytosis is elicited. Moore et al. PNAS-USA 84: 7134-7138 (1987).

Human G-CSF can be obtained and purified from a number of sources.Natural human G-CSF (nhG-CSF) can be isolated from the supernatants ofcultured human tumor cell lines. The development of recombinant DNAtechnology, see, for instance, U.S. Pat. No. 4,810,643 (Souza)incorporated herein by reference, has enabled the production ofcommercial scale quantities of G-CSF in glycosylated form as a productof eukaryotic host cell expression, and of G-CSF in non-glycosylatedform as a product of prokaryotic host cell expression.

G-CSF has been found to be useful in the treatment of indications wherean increase in neutrophils will provide benefits. For example, forcancer patients, G-CSF is beneficial as a means of selectivelystimulating neutrophil production to compensate for hematopoieticdeficits resulting from chemotherapy or radiation therapy. Otherindications include treatment of various infectious diseases and relatedconditions, such as sepsis, which is typically caused by a metabolite ofbacteria. G-CSF is also useful alone, or in combination with othercompounds, such as other cytokines, for growth or expansion of cells inculture, for example, for bone marrow transplants.

Signal transduction, the way in which G-CSF effects cellular metabolism,is not currently thoroughly understood. G-CSF binds to a cell-surfacereceptor which apparently initiates the changes within particularprogenitor cells, leading to cell differentiation.

Various altered G-CSF's have been reported. Generally, for design ofdrugs, certain changes are known to have certain structural effects. Forexample, deleting one cysteine could result in the unfolding of amolecule which is, in its unaltered state, is normally folded via adisulfide bridge. There are other known methods for adding, deleting orsubstituting amino acids in order to change the function of a protein.

Recombinant human G-CSF mutants have been prepared, but the method ofpreparation does not include overall structure/function relationshipinformation. For example, the mutation and biochemical modification ofCys¹⁸ has been reported. Kuga et al. Biochem. Biophy. Res. Comm 159:103-111 (1989); Lu et al. Arch. Biochem. Biophys. 268: 81-92 (1989).

In U.S. Pat. No. 4,810,643, entitled, “Production of PluripotentGranulocyte Colony-Stimulating Factor” (as cited above), polypeptideanalogs and peptide fragments of G-CSF are disclosed generally. SpecificG-CSF analogs disclosed include those with the cysteins at positions 17,36, 42, 64, and 74 (of the 174 amino acid species or of those having 175amino acids, the additional amino acid being an N-terminal methionine)substituted with another amino acid, (such as serine), and G-CSF with analanine in the first (N-terminal) position.

EP 0 335 423 entitled “Modified human G-CSF” reportedly discloses themodification of at least one amino group in a polypeptide having hG-CSFactivity.

EP 0 272 703 entitled “Novel Polypeptide” reportedly discloses G-CSFderivatives having an amino acid substituted or deleted at or “in theneighborhood” of the N-terminus.

EP 0 459 630, entitled “Polypeptides” reportedly discloses derivativesof naturally occurring G-CSF having at least one of the biologicalproperties of naturally occurring G-CSF and a solution stability of atleast 35% at 5 mg/ml in which the derivative has at least Cys¹⁷ of thenative sequence replaced by a Ser¹⁷ residue and Asp²⁷ of the nativesequence replaced by a Ser²⁷ residue.

EP 0 256 843 entitled “Expression of G-CSF and Muteins Thereof and TheirUses” reportedly discloses a modified DNA sequence encoding G-CSFwherein the N-terminus is modified for enhanced expression of protein inrecombinant host cells, without changing the amino acid sequence of theprotein.

EP 0 243 153 entitled “Human G-CSF Protein Expression” reportedlydiscloses G-CSF to be modified by inactivating at least one yeast KEX2protease processing site for increased yield in recombinant productionusing yeast.

Shaw, U.S. Pat. No. 4,904,584, entitled “Site-Specific HomogeneousModification of Polypeptides,” reportedly discloses lysine alteredproteins.

WO/9012874 reportedly discloses cysteine altered variants of proteins.

Australian patent application Document No. AU-A-10948/92, entitled,“Improved Activation of Recombinant Proteins” reportedly discloses theaddition of amino acids to either terminus of a G-CSF molecule for thepurpose of aiding in the folding of the molecule after prokaryoticexpression.

Australian patent application Document No. AU-A-76380/91, entitled,“Muteins of the Granulocyte Colony Stimulating Factor (G-CSF)”reportedly discloses muteins of the granulocyte stimulating factor G-CSFin the sequence Leu-Gly-His-Ser-Leu-Gly-Ile at position 50-56 of G-CSFwith 174 amino acids, and position 53 to 59 of the G-CSF with 177 aminoacids, or/and at least one of the four histadine residues at positions43, 79, 156 and 170 of the mature G-CSF with 174 amino acids or atpositions 46, 82, 159, or 173 of the mature G-CSF with 177 amino acids.

GB 2 213 821, entitled “Synthetic Human Granulocyte Colony StimulatingFactor Gene” reportedly discloses a synthetic G-CSF-encoding nucleicacid sequence incorporating restriction sites to facilitate the cassettemutagenesis of selected regions, and flanking restriction sites tofacilitate the incorporation of the gene into a desired expressionsystem.

G-CSF has reportedly been crystallized to some extent, i.e., EP 344 796,and the overall structure of G-CSF has been surmised, but only on agross level. Bazan, Immunology Today 11: 350-354 (1990); Parry et al. J.Molecular Recognition 8: 107-110 (1988). To date, there have been noreports of the overall structure of G-CSF, and no systematic studies ofthe relationship of the overall structure and function of the molecule,studies which are essential to the systematic design of G-CSF analogs.

Accordingly, there exists a need for a method of this systematic designof G-CSF analogs, and the resultant compositions.

SUMMARY OF THE INVENTION

The three dimensional structure of G-CSF has now been determined to theatomic level. From this three-dimensional structure, one can nowforecast with substantial certainty how changes in the composition of aG-CSF molecule may result in structural changes. These structuralcharacteristics may be correlated with biological activity to design andproduce G-CSF analogs.

Although others had speculated regarding the three dimensional structureof G-CSF, Bazan, Immunology Today 11: 350-354 (1990); Parry et al. J.Molecular Recognition 8: 107-110 (1988), these speculations were of nohelp to those wishing to prepare G-CSF analogs either because thesurmised structure was incorrect (Parry et al., supra) and/or becausethe surmised structure provided no detail correlating the constituentmoieties with structure. The present determination of thethree-dimensional structure to the atomic level is by far the mostcomplete analysis to date, and provides important information to thosewishing to design and prepare G-CSF analogs. For example, from thepresent three dimensional structural analysis, precise areas ofhydrophobicity and hydrophilicity have been determined.

Relative hydrophobicity is important because it directly relates to thestability of the molecule. Generally, biological molecules, found inaqueous environments, are externally hydrophilic and internallyhydrophobic; in accordance with the second law of thermodynamicsprovides, this is the lowest energy state and provides for stability.Although one could have speculated that G-CSF's internal core would behydrophobic, and the outer areas would be hydrophilic, one would havehad no way of knowing specific hydrophobic or hydrophilic areas. Withthe presently provided knowledge of areas of hydrophobicity/philicity,one may forecast with substantial certainty which changes to the G-CSFmolecule will affect the overall structure of the molecule.

As a general rule, one may use knowledge of the geography of thehydrophobic and hydrophilic regions to design analogs in which theoverall G-CSF structure is not changed, but change-does affectbiological activity (“biological activity” being used here in itsbroadest sense to denote function). One may correlate biologicalactivity to structure. If the structure is not changed, and the mutationhas no effect on biological activity, then the mutation has nobiological function. If, however, the structure is not changed and themutation does affect biological activity, then the residue (or atom) isessential to at least one biological function. Some of the presentworking examples were designed to provide no change in overallstructure, yet have a change in biological function.

Based on the correlation of structure to biological activity, one aspectof the present invention relates to G-CSF analogs. These analogs aremolecules which have more, fewer, different or modified amino acidresidues from the G-CSF amino acid sequence. The modifications may be byaddition, substitution, or deletion of one or more amino acid residues.The modification may include the addition or substitution of analogs ofthe amino acids themselves, such as peptidomimetics or amino acids withaltered moieties such as altered side groups. The G-CSF used as a basisfor comparison may be of human, animal or recombinant nucleicacid-technology origin (although the working examples disclosed hereinare based on the recombinant production of the 174 amino acid species ofhuman G-CSF, having an extra N-terminus methionyl residue). The analogsmay possess functions different from natural human G-CSF molecule, ormay exhibit the same functions, or varying degrees of the samefunctions. For example, the analogs may be designed to have a higher orlower biological activity, have a longer shelf-life or a decrease instability, be easier to formulate, or more difficult to combine withother ingredients. The analogs may have no hematopoietic activity, andmay therefore be useful as an antagonist against G-CSF effect (as, forexample, in the overproduction of G-CSF). From time to time herein thepresent analogs are referred to as proteins or peptides for convenience,but contemplated herein are other types of molecules, such aspeptidomimetics or chemically modified peptides.

In another aspect, the present invention relates to related compositionscontaining a G-CSF analog as an active ingredient. The term, “relatedcomposition,” as used herein, is meant to denote a composition which maybe obtained once the identity of the G-CSF analog is ascertained (suchas a G-CSF analog labeled with a detectable label, related receptor orpharmaceutical composition). Also considered a related composition arechemically modified versions of the G-CSF analog, such as those havingattached at least one polyethylene glycol molecule.

For example, one may prepare a G-CSF analog to which a detectable labelis attached, such as a fluorescent, chemiluminescent or radioactivemolecule.

Another example is a pharmaceutical composition which may be formulatedby known techniques using known materials, see, Remington'sPharmaceutical Sciences, 18th Ed. (1990, Mack Publishing Co., Easton,Pa. 18042) pp. 1435-1712, which are herein incorporated by reference.Generally, the formulation will depend on a variety of factors such asadministration, stability, production concerns and other factors. TheG-CSF analog may be administered by injection or by pulmonaryadministration via inhalation. Enteric dosage forms may also beavailable for the present G-CSF analog compositions, and therefore oraladministration may be effective. G-CSF analogs may be inserted intoliposomes or other microcarriers for delivery, and may be formulated ingels or other compositions for sustained release. Although preferredcompositions will vary depending on the use to which the compositionwill be put, generally, for G-CSF analogs having at least one of thebiological activities of natural G-CSF, preferred pharmaceuticalcompositions are those prepared for subcutaneous injection or forpulmonary administration via inhalation, although the particularformulations for each type of administration will depend on thecharacteristics of the analog.

Another example of related composition is a receptor for the presentanalog. As used herein, the term “receptor” indicates a moiety whichselectively binds to the present analog molecule. For example,antibodies, or fragments thereof, or “recombinant antibodies” (see Huseet al. Science 246: 1275 (1989)) may be used as receptors. Selectivebinding does not mean only specific binding (although binding-specificreceptors are encompassed herein), but rather that the binding is not arandom event. Receptors may be on the cell surface or intra- orextra-cellular, and may act to effectuate, inhibit or localize thebiological activity of the present analogs. Receptor binding may also bea triggering mechanism for a cascade of activity indirectly related tothe analog itself. Also contemplated herein are nucleic acids, vectorscontaining such nucleic acids and host cells containing such nucleicacids which encode such receptors.

Another example of a related composition is a G-CSF analog with achemical moiety attached. Generally, chemical modification may alterbiological activity or antigenicity of a protein, or may alter othercharacteristics, and these factors will be taken into account by askilled practitioner. As noted above, one example of such chemicalmoiety is polyethylene glycol. Modification may include the addition ofone or more hydrophilic or hydrophobic polymer molecules, fatty acidmolecules, or polysaccharide molecules. Examples of chemical modifiersinclude polyethylene glycol, alklpolyethylene glycols, DI-poly(aminoacids), polyvinylpyrrolidone, polyvinyl alcohol, pyran copolymer, aceticacid/acylation, proprionic acid, palmitic acid, stearic acid, dextran,carboxymethyl cellulose, pullulan, or agarose. See, Francis, Focus onGrowth Factors 3: 4-10 (May 1992)(published by Mediscript, MountviewCourt, Friern Barnet Lane, London N20 OLD, UK). Also, chemicalmodification may include an additional protein or portion thereof, useof a cytotoxic agent, or an antibody. The chemical modification may alsoinclude lecithin.

In another aspect, the present invention relates to nucleic acidsencoding such analogs. The nucleic acids may be DNAs or RNAs orderivatives thereof, and will typically be cloned and expressed on avector, such as a phage or plasmid containing appropriate regulatorysequences. The nucleic acids may be labeled (such as using aradioactive, chemiluminescent, or fluorescent label) for diagnostic orprognostic purposes, for example. The nucleic acid sequence may beoptimized for expression, such as including codons preferred forbacterial expression. The nucleic acid and its complementary strand, andmodifications thereof which do not prevent encoding of the desiredanalog are here contemplated.

In another aspect, the present invention relates to host cellscontaining the above nucleic acids encoding the present analogs. Hostcells may be eukaryotic or prokaryotic, and expression systems mayinclude extra steps relating to the attachment (or prevention) of sugargroups (glycosylation), proper folding of the molecule, the addition ordeletion of leader sequences or other factors incident to recombinantexpression.

In another aspect the present invention relates to antisense nucleicacids which act to prevent or modify the type or amount of expression ofsuch nucleic acid sequences. These may be prepared by known methods.

In another aspect of the present invention, the nucleic acids encoding apresent analog may be used for gene therapy purposes, for example, byplacing a vector containing the analog-encoding sequence into arecipient so the nucleic acid itself is expressed inside the recipientwho is in need of the analog composition. The vector may first be placedin a carrier, such as a cell, and then the carrier placed into therecipient. Such expression may be localized or systemic. Other carriersinclude non-naturally occurring carriers, such as liposomes or othermicrocarriers or particles, which may act to mediate gene transfer intoa recipient.

The present invention also provides for computer programs for theexpression (such as visual display) of the G-CSF or analog threedimensional structure, and further, a computer program which expressesthe identity of each constituent of a G-CSF molecule and the preciselocation within the overall structure of that constituent, down to theatomic level. Set forth below is one example of such program. There aremany currently available computer programs for the expression of thethree dimensional structure of a molecule. Generally, these programsprovide for inputting of the coordinates for the three dimensionalstructure of a molecule (i.e., for example, a numerical assignment foreach atom of a G-CSF molecule along an x, y, and z axis), means toexpress (such as visually display) such coordinates, means to alter suchcoordinates and means to express an image of a molecule having suchaltered coordinates. One may program crystallographic information, i.e.,the coordinates of the location of the atoms of a G-CSF molecule inthree dimension space, wherein such coordinates have been obtained fromcrystallographic analysis of said G-CSF molecule, into such programs togenerate a computer program for the expression (such as visual display)of the G-CSF three dimensional structure. Also provided, therefore, is acomputer program for the expression of G-CSF analog three dimensionalstructure. Preferred is the computer program Insight II, version 4,available from Biosym, San Diego, Calif., with the coordinates as setforth in FIG. 5 input. Preferred expression means is on a SiliconGraphics 320 VGX computer, with Crystal Eyes glasses (also availablefrom Silicon Graphics), which allows one to view the G-CSF molecule orits analog stereoscopically. Alternatively, the present G-CSFcrystallographic coordinates and diffraction data are also deposited inthe Protein Data Bank, Chemistry Department, Brookhaven NationalLaboratory, Upton, N.Y. 19723, USA. One may use these data in preparinga different computer program for expression of the three dimensionalstructure of a G-CSF molecule or analog thereof. Therefore, anotheraspect of the present invention is a computer program for the expressionof the three dimensional structure of a G-CSF molecule. Also provided issaid computer program for visual display of the three dimensionalstructure of a G-CSF molecule; and further, said program having meansfor altering such visual display. Apparatus useful for expression ofsuch computer program, particularly for the visual display of thecomputer image of said three dimensional structure of a G-CSF moleculeor analog thereof is also therefore here provided, as well as means forpreparing said computer program and apparatus.

The computer program is useful for preparation of G-CSF analogs becauseone may select specific sites on the G-CSF molecule for alteration andreadily ascertain the effect the alteration will have on the overallstructure of the G-CSF molecule. Selection of said site for alterationwill depend on the desired biological characteristic of the G-CSFanalog. If one were to randomly change said G-CSF molecule(r-met-hu-G-CSF) there would be 175²⁰ possible substitutions, and evenmore analogs having multiple changes, additions or deletions. By viewingthe three dimensional structure wherein said structure is correlatedwith the composition of the molecule, the selection for sites ofalteration is no longer a random event, but sites for alteration may bedetermined rationally.

As set forth above, identity of the three dimensional structure ofG-CSF, including the placement of each constituent down to the atomiclevel has now yielded information regarding which moieties are necessaryto maintain the overall structure of the G-CSF molecule. One maytherefore select whether to maintain the overall structure of the G-CSFmolecule when preparing a G-CSF analog of the present invention, orwhether (and how) to change the overall structure of the G-CSF moleculewhen preparing a G-CSF analog of the present invention. Optionally, onceone has prepared such analog, one may test such analog for a desiredcharacteristic.

One may, for example, seek to maintain the overall structure possessedby a non-altered natural or recombinant G-CSF molecule. The overallstructure is presented in FIGS. 2, 3, and 4, and is described in moredetail below. Maintenance of the overall structure may ensure receptorbinding, a necessary characteristic for an analog possessing thehematopoietic capabilities of natural G-CSF (if no receptor binding,signal transduction does not result from the presence of the analog). Itis contemplated that one class of G-CSF analogs will possess the threedimensional core structure of a natural or recombinant (non-altered)G-CSF molecule, yet possess different characteristics, such as anincreased ability to selectively stimulate neutrophils. Another class ofG-CSF analogs are those with a different overall structure whichdiminishes the ability of a G-CSF analog molecule to bind to a G-CSFreceptor, and possesses a diminished ability to selectively stimulateneutrophils as compared to non-altered natural or recombinant G-CSF.

For example, it is now known which moieties within the internal regionsof the G-CSF molecule are hydrophobic, and, correspondingly, whichmoieties on the external portion of the G-CSF molecule are hydrophilic.Without knowledge of the overall three dimensional structure, preferablyto the atomic level as provided herein, one could not forecast whichalterations within this hydrophobic internal area would result in achange in the overall structural conformation of the molecule. Anoverall structural change could result in a functional change, such aslack of receptor binding, for example, and therefore, diminishment ofbiological activity as found in non-altered G-CSF. Another class ofG-CSF analogs is therefore G-CSF analogs which possess the samehydrophobicity as (non-altered) natural or recombinant G-CSF. Moreparticularly, another class of G-CSF analogs possesses the samehydrophobic moieties within the four helical bundle of its internal coreas those hydrophobic moieties possessed by (non-altered) natural orrecombinant G-CSF yet have a composition different from said non-alterednatural or recombinant G-CSF.

Another example relates to external loops which are structures whichconnect the internal core (helices) of the G-CSF molecule. From thethree dimensional structure—including information regarding the spatiallocation of the amino acid residues—one may forecast that certainchanges in certain loops will not result in overall conformationalchanges. Therefore, another class of G-CSF analogs provided herein isthat having an altered external loop but possessing the same overallstructure as (non-altered) natural or recombinant G-CSF. Moreparticularly, another class of G-CSF analogs provided herein are thosehaving an altered external loop, said loop being selected from the looppresent between helices A and B; between helices B and C; betweenhelices C and D; between helices D and A, as those loops and helices areidentified herein. More particularly, said loops, preferably the AB loopand/or the CD loop are altered to increase the half life of the moleculeby stabilizing said loops. Such stabilization may be by connecting allor a portion of said loop(s) to a portion of an alpha helical bundlefound in the core of a G-CSF (or analog) molecule. Such connection maybe via beta sheet, salt bridge, disulfide bonds, hydrophobic interactionor other connecting means available to those skilled in the art, whereinsuch connecting means serves to stabilize said external loop or loops.For example, one may stabilize the AB or CD loops by connecting the ABloop to one of the helices within the internal region of the molecule.

The N-terminus also may be altered without change in the overallstructure of a G-CSF molecule, because the N-terminus does not effectstructural stability of the internal helices, and, although the externalloops are preferred for modification, the same general statements applyto the N-terminus.

Additionally, such external loops may be the site(s) for chemicalmodification because in (non-altered) natural or recombinant G-CSF suchloops are relatively flexible and tend not to interfere with receptorbinding. Thus, there would be additional room for a chemical moiety tobe directly attached (or indirectly attached via another chemical moietywhich serves as a chemical connecting means). The chemical moiety may beselected from a variety of moieties available for modification of one ormore function of a G-CSF molecule. For example, an external loop mayprovide sites for the addition of one or more polymer which serves toincrease serum half-life, such as a polyethylene glycol molecule. Suchpolyethylene glycol molecule(s) may be added wherein said loop isaltered to include additional lysines which have reactive side groups towhich polyethylene glycol moieties are capable of attaching. Otherclasses of chemical moieties may also be attached to one or moreexternal loops, including but not limited to other biologically activemolecules, such as receptors, other therapeutic proteins (such as otherhematopoietic factors which would engender a hybrid molecule), orcytotoxic agents (such as diphtheria toxin). This list is of course notcomplete; one skilled in the art possessed of the desired chemicalmoiety will have the means to effect attachment of said desired moietyto the desired external loop. Therefore, another class of the presentG-CSF analogs includes those with at least one alteration in an externalloop wherein said alteration provides for the addition of a chemicalmoiety such as at least one polyethylene glycol molecule.

Deletions, such as deletions of sites recognized by proteins fordegradation of the molecule, may also be effectual in the externalloops. This provides alternative means for increasing half-life of amolecule otherwise having the G-CSF receptor binding and signaltransduction capabilities (i.e., the ability to selectively stimulatethe maturation of neutrophils). Therefore, another class of the presentG-CSF analogs includes those with at least one alteration in an externalloop wherein said alteration decreases the turnover of said analog byproteases. Preferred loops for such alterations are the AB loop and theCD loop. One may prepare an abbreviated G-CSF molecule by deleting aportion of the amino acid residues found in the external loops(identified in more detail below), said abbreviated G-CSF molecule mayhave additional advantages in preparation or in biological function.

Another example relates to the relative charges between amino acidresidues which are in proximity to each other. As noted above, the G-CSFmolecule contains a relatively tightly packed four helical-bundle. Someof the faces on the helices face other helices. At the point (such as aresidue) where a helix faces another helix, the two amino acid moietieswhich face each other may have the same charge, and thus tend to repeleach other, which lends instability to the overall molecule. This may beeliminated by changing the charge (to an opposite charge or a neutralcharge) of one or both of the amino acid moieties so that there is norepelling. Therefore, another class of G-CSF analogs includes thoseG-CSF analogs having been altered to modify instability due to surfaceinteractions, such as electron charge location.

In another aspect, the present invention relates to methods fordesigning G-CSF analogs and related compositions and the products ofthose methods. The end products of the methods may be the G-CSF analogsas defined above or related compositions. For instance, the examplesdisclosed herein demonstrate (a) the effects of changes in theconstituents (i.e., chemical moieties) of the G-CSF molecule on theG-CSF structure, and (b) the effects of changes in structure onbiological function. Essentially, therefore, another aspect of thepresent invention is a method for preparing a G-CSF analog comprisingthe steps of:

-   -   (a) viewing information conveying the three dimensional        structure of a G-CSF molecule wherein the chemical moieties,        such as each amino acid residue or each atom of each amino acid        residue, of the G-CSF molecule are correlated with said        structure,    -   (b) selecting from said information a site on a G-CSF molecule        for alteration;    -   (c) preparing a G-CSF analog molecule having such alteration;        and    -   (d) optionally, testing such G-CSF analog molecule for a desired        characteristic.

One may use the here provided computer programs for a computer-basedmethod for preparing a G-CSF analog. Another aspect of the presentinvention is therefore a computer based method for preparing a G-CSFanalog comprising the steps of:

-   -   (a) providing computer expression of the three dimensional        structure of a G-CSF molecule wherein the chemical moieties,        such as each amino acid residue or each atom of each amino acid        residue, of the G-CSF molecule are correlated with said        structure;    -   (b) selecting from said computer expression a site on a G-CSF        molecule for alteration;    -   (c) preparing a G-CSF molecule having such alteration; and,    -   (d) optionally, testing such G-CSF molecule for a desired        characteristic.

More specifically, the present invention provides a method for preparinga G-CSF analog comprising the steps of:

-   -   (a) viewing the three dimensional structure of a G-CSF molecule        via a computer, said computer programmed (i) to express the        coordinates of a G-CSF molecule in three dimensional space,        and (ii) to allow for entry of information for alteration of        said G-CSF expression and viewing thereof;    -   (b) selecting a site on said visual image of said G-CSF molecule        for alteration;    -   (c) entering information for said alteration on said computer;    -   (d) viewing a three dimensional structure of said altered G-CSF        molecule via said computer;    -   (e) optionally repeating steps (a)-(e);    -   (f) preparing a G-CSF analog with said alteration; and    -   (g) optionally testing said G-CSF analog for a desired        characteristic.

In another aspect, the present invention relates to methods of using thepresent G-CSF analogs and related compositions and methods for thetreatment or protection of mammals, either alone or in combination withother hematopoietic factors or drugs in the treatment of hematopoieticdisorders. It is contemplated that one aspect of designing G-CSF analogswill be the goal of enhancing or modifying the characteristicsnon-modified G-CSF is known to have. For example, the present analogsmay possess enhanced or modified activities, so, where G-CSF is usefulin the treatment of (for example) neutropenia, the present compositionsand methods may also be of such use.

Another example is the modification of G-CSF for the purpose ofinteracting more effectively when used in combination with other factorsparticularly in the treatment of hematopoietic disorders. One example ofsuch combination use is to use an early-acting hematopoietic factor(i.e., a factor which acts earlier in the hematopoiesis cascade onrelatively undifferentiated cells) and either simultaneously or inseriatim use of a later-acting hematopoietic factor, such as G-CSF oranalog thereof (as G-CSF acts on the CFU-GM lineage in the selectivestimulation of neutrophils). The present methods and compositions may beuseful in therapy involving such combinations or “cocktails” ofhematopoietic factors.

The present compositions and methods may also be useful in the treatmentof leukopenia, mylogenous leukemia, severe chronic neutropenia, aplasticanemia, glycogen storage disease, mucosistitis, and other bone marrowfailure states. The present compositions and methods may also be usefulin the treatment of hematopoietic deficits arising from chemotherapy orfrom radiation therapy. The success of bone marrow transplantation, orthe use of peripheral blood progenitor cells for transplantation, forexample, may be enhanced by application of the present compositions(proteins or nucleic acids for gene therapy) and methods. The presentcompositions and methods may also be useful in the treatment ofinfectious diseases, such in the context of wound healing, burntreatment, bacteremia, septicemia, fungal infections, endocarditis,osteopyelitis, infection related to abdominal trauma, infections notresponding to antibiotics, pneumonia and the treatment of bacterialinflammation may also benefit from the application of the presentcompositions and methods. In addition, the present compositions andmethods may be useful in the treatment of leukemia based upon a reportedability to differentiate leukemic cells. Welte et al. PNAS-USA 82:1526-1530 (1985). Other applications include the treatment ofindividuals with tumors, using the present compositions and methods,optionally in the presence of receptors (such as antibodies) which bindto the tumor cells. For review articles on therapeutic applications, seeLieshhke et al. N. Engl. J. Med. 327: 28-34, 99-106 (1992) both of whichare herein incorporated by reference.

The present compositions and methods may also be useful to act asintermediaries in the production of other moieties; for example, G-CSFhas been reported to influence the production of other hematopoieticfactors and this function (if ascertained) may be enhanced or modifiedvia the present compositions and/or methods.

The compositions related to the present G-CSF analogs, such asreceptors, may be useful to act as an antagonist which prevents theactivity of G-CSF or an analog. One may obtain a composition with someor all of the activity of non-altered G-CSF or a G-CSF analog, and addone or more chemical moieties to alter one or more properties of suchG-CSF or analog. With knowledge of the three dimensional conformation,one may forecast the best geographic location for such chemicalmodification to achieve the desired effect.

General objectives in chemical modification may include improvedhalf-life (such as reduced renal, immunological or cellular clearance),altered bioactivity (such as altered enzymatic properties, dissociatedbioactivities or activity in organic solvents), reduced toxicity (suchas concealing toxic epitopes, compartmentalization, and selectivebiodistribution), altered immunoreactivity (reduced immunogenicity,reduced antigenicity or adjuvant action), or altered physical properties(such as increased solubility, improved thermal stability, improvedmechanical stability, or conformational stabilization). See Francis,Focus on Growth Factors 3: 4-10 (May 1992)(published by Mediscript,Mountview Court, Friern Barnet Lane, London N20 OLD, UK).

The examples below are illustrative of the present invention and are notintended as a limitation. It is understood that variations andmodifications will occur to those skilled in the art, and it is intendedthat the appended claims cover all such equivalent variations which comewithin the scope of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the amino acid sequence of the 174 aminoacid species of G-CSF with an additional N-terminal methionine (Seq. ID.No. 2).

FIGS. 2A-2G are a topology diagrams of the crystalline structure ofG-CSF, as well as hGH, pGH, GM-CSF, INF-β, IL-2, and IL-4. Theseillustrations are based on inspection of cited references. The length ofsecondary structural elements are drawn in proportion to the number ofresidues. A, B, C, and D helices are labeled according to the schemeused herein for G-CSF. For INF-β, the original labeling of helices isindicated in parentheses.

FIG. 3 is an “ribbon diagram” of the three dimensional structure ofG-CSF. Helix A is amino acid residues 11-39 (numbered according to FIG.1, above Seq. ID. No. 2), helix B is amino acid residues 72-91, helix Cis amino acid residues 100-123, and helix D is amino acid residues143-173. The relatively short 3¹⁰ helix is at amino acid residues 45-48,and the alpha helix is at amino acid residues 48-53. Residues 93-95 formalmost one turn of a left handed helix.

FIG. 4 is a “barrel diagram” of the three dimensional structure ofG-CSF. Shown in various shades of gray are the overall cylinders andtheir orientations for the three dimensional structure of G-CSF. Thenumbers indicate amino acid residue position according to FIG. 1 (Seq.ID. No. 2) above.

FIGS. 5A-5VV is a list of the coordinates used to generate acomputer-aided visual image of the three dimensional structure of G-CSF.The coordinates are set forth below. The columns correspond to separatefield:

-   -   (i) Field 1 (from the left hand side) is the atom,    -   (ii) Field 2 is the assigned atom number,    -   (iii) Field 3 is the atom name (according to the periodic table        standard nomenclature, with CB being carbon atom Beta, CG is        Carbon atom Gamma, etc.);    -   (iv) Field 4 is the residue type (according to three letter        nomenclature for amino acids as found in, i.e., Stryer,        Biochemistry, 3d Ed., W.H. Freeman & Co., New York 1988, inside        back cover);    -   (v) Fields 5-7 are the x-axis, y-axis and z-axis positions of        the atom;    -   (vi) Field 8 (often a “1.00”) designates occupancy at that        position;    -   (vii) Field 9 designates the B-factor;    -   (viii) Field 10 designates the molecule designation three        molecules (designated a, b, and c) of G-CSF crystallized        together as a unit. The designation a, b, or c indicates which        coordinates are from which molecule. The number after the letter        (1, 2, or 3) indicates the assigned amino acid residue position,        with molecule A having assigned positions 10-175, molecule B        having assigned positions 210-375, and molecule C having        assigned positions 410-575. These positions were so designated        so that there would be no overlap among the three molecules        which crystallized together. (The “W” designation indicates        water).

FIGS. 6A-6C are schematic representations of the strategy involved inrefining the crystallization matrix for parameters involved incrystallization. The crystallization matrix corresponds to the finalconcentration of the components (salts, buffers and precipitants) of thecrystallization solutions in the wells of a 24 well tissue cultureplate. These concentrations are produced by pipetting the appropriatevolume of stock solutions into the wells of the microtiter plate. Todesign the matrix, the crystallographer decides on an upper and lowerconcentration of the component. These upper and lower concentrations canbe pipetted along either the rows (i.e., A1-A6, B1-B6, C1-C6 or D1-D6)or along the entire tray (A1-D6). The former method is useful forchecking reproducibility of crystal growth of a single component along alimited number of wells, whereas the later method is more useful ininitial screening. The results of several stages of refinement of thecrystallization matrix are illustrated by a representation of threeplates. The increase in shading in the wells indicates a positivecrystallization result which, in the final stages, would be X-rayquality crystals but in the initial stages could be oil droplets,granular precipitates or small crystals approximately less than 0.05 mmin size. Part A represents an initial screen of one parameter in whichthe range of concentration between the first well (A1) and last well(D6) is large and the concentration increase between wells is calculatedas ((concentration A1)−(concentration D6))/23). Part B represents thatin later stages of the crystallization matrix refinement of theconcentration spread between A1 and D6 would be reduced which wouldresult in more crystals formed per plate. Part C indicates a final stageof matrix refinement in which quality crystals are found in most wellsof the plate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention grows out of the discovery of the threedimensional structure of G-CSF. This three dimensional structure hasbeen expressed via computer program for stereoscopic viewing. By viewingthis stereoscopically, structure-function relationships identified andG-CSF analogs have been designed and made.

The Overall Three Dimensional Structure of G-CSF

The G-CSF used to ascertain the structure was a non-glycosylated 174amino acid species having an extra N-terminal methionine residueincident to bacterial expression. The DNA (Seq. ID. No. 1) and aminoacid sequence (Seq. ID. No. 2) of this G-CSF are illustrated in FIG. 1.

Overall, the three dimensional structure of G-CSF is predominantlyhelical, with 103 of the 175 residues forming a 4-alpha-helical bundle.The only other secondary structure is found in the loop between thefirst two long helices where a 4 residue 3¹⁰ helix is immediatelyfollowed by a 6 residue alpha helix. As shown in FIG. 2, the overallstructure has been compared with the structure reported for otherproteins: growth hormone (Abdel-Meguid et al. PNAS-USA 84: 6434 (1987)and Vos et al. Science 255: 305-312 (1992)), granulocyte macrophagecolony stimulating factor (Diederichs et al. Science 254: 1779-1782(1991)), interferon-β (Senda et al. EMBO J. 11: 3193-3201 (1992)),interleukin-2 (McKay Science 257: 1673-1677 (1992)) and interleukin-4(Powers et al. Science 256: 1673-1677 (1992), and Smith et al. J. Mol.Biol. 224: 899-904 (1992)). Structural similarity among these growthfactors occurs despite the absence of similarity in their amino acidsequences.

Presently, the structural information was correlation of G-CSFbiochemistry, and this can be summarized as follows (with sequenceposition 1 being at the N-terminus):

TABLE 1 Sequence Position Description of Structure Analysis  1-10Extended chain Deletion causes no loss of biological activity Cys¹⁸Partially buried Reactive with DTNB and Thimersososl but not withiodo-acetate 34 Alternative splice site Insertion reduces biologicalactivity  20-47 (inclusive) Helix A, first disulfide Predicted receptorand portion of AB helix binding region based on neutralizing antibodydata 20, 23, 24 Helix A Single alanine mutation of residue(s) reducesbiological activity. Predicted receptor binding (Site B). 165-175(inclusive) Carboxy terminus Deletion reduces biological activity

This biochemical information, having been gleaned from antibody bindingstudies, see Layton et al. Biochemistry 266: 23815-23823 (1991), wassuperimposed on the three-dimensional structure in order to design G-CSFanalogs. The design, preparation, and testing of these G-CSF analogs isdescribed in Example 1 below.

Example 1

This Example describes the preparation of crystalline G-CSF, thevisualization of the three dimensional structure of recombinant humanG-CSF via computer-generated image, the preparation of analogs, usingsite-directed mutagenesis or nucleic acid amplification methods, thebiological assays and HPLC analysis used to analyze the G-CSF analogs,and the resulting determination of overall structure/functionrelationships. All cited publications are herein incorporated byreference.

A. Use of Automated Crystallization

The need for a three-dimensional structure of recombinant humangranulocyte colony stimulating factor (r-hu-G-CSF), and the availabilityof large quantities of the purified protein, led to methods of crystalgrowth by incomplete factorial sampling and seeding. Starting with theimplementation of incomplete factorial crystallization described byJancarik et al. J. Appl. Crystallogr. 24: 409 (1991) solution conditionsthat yielded oil droplets and birefringence aggregates were ascertained.Also, software and hardware of an automated pipetting system weremodified to produce some 400 different crystallization conditions perday. Weber J. Appl. Crystallogr. 20: 366-373 (1987). This procedure ledto a crystallization solution which produced r-hu-G-CSF crystals.

The size, reproducibility and quality of the crystals was improved by aseeding method in which the number of “nucleation initiating units” wasestimated by serial dilution of a seeding solution. These methodsyielded reproducible growth of 2.0 mm r-hu-G-CSF crystals. The spacegroup of these crystals is P2₁2₁2₁ with cell dimensions of a=90 Å, b=110Å and c=49 Å, and they diffract to a resolution of 2.0 Å.

1. Overall Methodology

To search for the crystallizing conditions of a new protein, Carter etal. J. Biol. Chem. 254: 122219-12223 (1979) proposed the incompletefactorial method. They suggested that a sampling of a large number ofrandomly selected, but generally probable, crystallizing conditions maylead to a successful combination of reagents that produce proteincrystallization. This idea was implemented by Jancarik et al. J. Appl.Crystallogr. 24: 409 (1991), who described 32 solutions for the initialcrystallization trials which cover a range of pH, salts andprecipitants. Here we describe an extension of their implementation toan expanded set of 70 solutions. To minimize the human effort and errorof solution preparation, the method has been programmed for an automaticpipetting machine.

Following Weber's method of successive automated grid searching (SAGS),J. Cryst. Growth 90: 318-324 (1988), the robotic system was used togenerate a series of solutions which continually refined thecrystallization conditions of temperature, pH, salts and precipitant.Once a solution that could reproducibly grow crystals was determined, aseeding technique which greatly improved the quality of the crystals wasdeveloped. When these methods were combined, hundreds of diffractionquality crystals (crystals diffracting to at least about 2.5 Angstroms,preferably having at least portions diffracting to below 2 Angstroms,and more preferably, approximately 1 Angstrom) were produced in a fewdays.

Generally, the method for crystallization, which may be used with anyprotein one desires to crystallize, comprises the steps of:

-   -   (a) combining aqueous aliquots of the desired protein with        either (i) aliquots of a salt solution, each aliquot having a        different concentration of salt; or (ii) aliquots of a        precipitant solution, each aliquot having a different        concentration of precipitant, optionally wherein each combined        aliquot is combined in the presence of a range of pH;    -   (b) observing said combined aliquots for precrystalline        formations, and selecting said salt or precipitant combination        and said pH which is efficacious in producing precrystalline        forms, or, if no precrystalline forms are so produced,        increasing the protein starting concentration &f said aqueous        aliquots of protein;    -   (c) after said salt or said precipitant concentration is        selected, repeating step (a) with said previously unselected        solution in the presence of said selected concentration; and    -   (d) repeating step (b) and step (a) until a crystal of desired        quality is obtained.

The above method may optionally be automated, which provides vastsavings in time and labor. Preferred protein starting concentrations arebetween 10 mg/ml and 20 mg/ml, however this starting concentration willvary with the protein (the G-CSF below was analyzed using 33 mg/ml). Apreferred range of salt solution to begin analysis with is (NaCl) of0-2.5M. A preferred precipitant is polyethylene glycol 8000, however,other precipitants include organic solvents (such as ethanol,),polyethylene glycol molecules having a molecular weight in the range of500-20,000, and other precipitants known to those skilled in the art.The preferred pH range is pH 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0,8.5, and 9.0. Precrystallization forms include oils, birefringementprecipitants, small crystals (<approximately 0.05 mm), medium crystals(approximately 0.5 to 0.5 mm) and large crystals (>approximately 0.5mm). The preferred time for waiting to see a crystalline structure is 48hours, although weekly observation is also preferred, and generally,after about one month, a different protein concentration is utilized(generally the protein concentration is increased). Automation ispreferred, using the Accuflex system as modified. The preferredautomation parameters are described below.

Generally, protein with a concentration between 10 mg/ml and 20 mg/mlwas combined with a range of NaCl solutions from 0-2.5M, and each suchcombination was performed (separately) in the presence of theabove-range of concentrations. Once a precrystallization structure isobserved, that salt concentration and pH range are optimized in aseparate experiment, until the desired crystal quality is achieved.Next, the precipitant concentration, in the presence of varying levelsof pH is also optimized. When both are optimized, the optimal conditionsare performed at once to achieve the desired result (this is diagrammedin FIG. 6).

a. Implementation of an Automated Pipetting System

Drops and reservoir solutions were prepared by an Accuflex pipettingsystem (ICN Pharmaceuticals, Costa Mesa, Calif.) which is controlled bya personal computer that sends ASCII codes through a standard serialinterface. The pipetter samples six different solutions by means of arotating valve and pipettes these solutions onto a plate whosetranslation in a x-y coordinate system can be controlled. The verticalcomponent of the system manipulates a syringe that is capable both ofdispensing and retrieving liquid.

The software provided with the Accuflex was based on the SAGS method asproposed by Cox et al. J. Appl. Crystallogr. 20: 366-373 (1987). Thismethod involves the systematic variation of two major crystallizationparameters, pH and precipitant concentration, with provision to vary twoothers. While building on these concepts, the software used hereprovided greater flexibility in the design and implementation of thecrystallization solutions used in the automated grid searching strategy.As a result of this flexibility the present software also created alarger number of different solutions. This is essential for theimplementation of the incomplete factorial method as described in thatsection below.

To improve the speed and design of the automated grid searchingstrategy, the Accuflex pipetting system required software and hardwaremodifications. The hardware changes allowed the use of two differentmicro-titer trays, one used for handing drop and one used for sittingdrop experiments, and a Plexiglas tray which held 24 additional buffer,salt and precipitant solutions. These additional solutions expanded thegrid of crystallizing conditions that could be surveyed.

To utilize the hardware modifications, the pipetting software waswritten in two subroutines; one subroutine allows the crystallographerto design a matrix of crystallization solutions based on theconcentrations of their components and the second subroutine totranslate these concentrations into the computer code which pipettes theproper volumes of the solutions into the crystallization trays. Theconcentration matrices can be generated by either of two programs. Thefirst program (MRF, available from Amgen Inc., Thousand Oaks, Calif.)refers to a list of stock solution concentrations supplied by thecrystallographer and calculates the required volume to be pipette toachieve the designated concentration. The second method, which ispreferred, incorporates a spread sheet program (Lotus™) which can beused to make more sophisticated gradients of precipitants or pH. Theconcentration matrix created by either program is interpreted by thecontrol program (SUX, a modification of the program found in theAccuflex pipetter originally and available from Amgen Inc., ThousandOaks, Calif.) and the wells are filled accordingly.

b. Implementation of the Incomplete Factorial Method

The convenience of the modified pipetting system for preparing diversesolutions improved the implementation of an expanded incompletefactorial method. The development of a new set of crystallizationsolutions having “random” components was generated using the programINFAC, Carter et al. J. Cryst. Growth 90: 60-73(1988) which produced alist containing 96 random combinations of one factor from threevariables. Combinations of calcium and phosphate which immediatelyprecipitated were eliminated, leaving 70 distinct combinations ofprecipitants, salts and buffers. These combinations were prepared usingthe automated pipetter and incubated for one week. The mixtures wereinspected and solutions which formed precipitants were prepared againwith lower concentrations of their components. This was repeated untilall wells were clear of precipitant.

c. Crystallization of r-hu-G-CSF

Several different crystallization strategies were used to find asolution which produced x-ray quality crystals. These strategiesincluded the use of the incomplete factorial method, refinement of thecrystallization conditions using successive automated grid searches(SAGS), implementation of a seeding technique and development of acrystal production procedure which yielded hundreds of quality crystalsovernight. Unless otherwise noted the screening and production ofr-hu-G-CSF crystals utilized the hanging drop vapor diffusion method.Afinsen et al. “Physical Principles Of Protein Crystallization.” In:Eisenberg (ed.), Advances in Protein Chemistry 41: 1-33 (1991).

The initial screening for crystallization conditions of r-hu-G-CSF usedthe Jancarik et al. J. Appl. Crystallogr. 24: 409 (1991) incompletefactorial method which resulted in several solutions that produced“precrystallization” results. These results included birefringentprecipitants, oils and very small crystals (<0.05 mm). Theseprecrystallizations solutions then served as the starting points forsystematic screening.

The screening process required the development of crystallizationmatrices. These matrices corresponded to the concentration of thecomponents in the crystallization solutions and were created using theIBM-PC based spread sheet Lotus™ and implemented with the modifiedAccuflex pipetting system. The strategy in designing the matrices was tovary one crystallization condition (such as salt concentration) whileholding the other conditions such as pH, and precipitant concentrationconstant. At the start of screening, the concentration range of thevaried condition was large but the concentration was successivelyrefined until all wells in the micro-titer tray produced the samecrystallization result. These results were scored as follows: crystals,birefringement precipitate, granular precipitate, oil droplets andamorphous mass. If the concentration of a crystallization parameter didnot produce at least a precipitant, the concentration of that parameterwas increased until a precipitant formed. After each tray was produced,it was left undisturbed for at least two days and then inspected forcrystal growth. After this initial screening, the trays were theninspected on a weekly basis.

From this screening process, two independent solutions with the same pHand precipitant but differing in salts (MgCl, LiSO₄) were identifiedwhich produced small (0.1×0.05×0.05 mm) crystals. Based on theseresults, a new series of concentration matrices were produced whichvaried MgCl with respect to LiSO₄ while keeping the othercrystallization parameters constant. This series of experiments resultedin identification of a solution which produced diffraction qualitycrystals (>approximately 0.5 mm) in about three weeks. To find thiscrystallization growth solution (100 mM Mes pH 5.8, 380 mM MgCl₂, 220 mMLiSO₄ and 8% PEG 8 k) approximately 8,000 conditions had been screenedwhich consumed about 300 mg of protein.

The size of the crystals depended on the number of crystals forming perdrop. Typically 3 to 5 crystals would be formed with average size of(1.0×0.7×0.7 mm). Two morphologies which had an identical space group(P2₁2₁2₁) and unit cell dimensions a=90.2, b=110.2, c=49.5 were obtaineddepending on whether or not seeding (see below) was implemented. Withoutseeding, the r-hu-G-CSF crystals had one long flat surface and roundededges.

When seeding was employed, crystals with sharp faces were observed inthe drop within 4 to 6 hours (0.05 by 0.05 by 0.05 mm). Within 24 hours,crystals had grown to (0.7 by 0.7 by 0.7 mm) and continued to growbeyond 2 mm depending on the number of crystals forming in the drop.

d. Seeding and Determination of Nucleation Initiation Sites.

The presently provided method for seeding crystals establishes thenumber of nucleation initiation units in each individual well used(here, after the optimum conditions for growing crystals had beendetermined). The method here is advantageous in that the number of“seeds” affects the quality of the crystals, and this in turn affectsthe degree of resolution. The present seeding here also providesadvantages in that with seeding, G-CSF crystal grows in a period ofabout three days, whereas without seeding, the growth takesapproximately three weeks.

In one series of production growth (see methods), showers of small butwell defined crystals were produced overnight (<0.01×0.01×0.01 mm).Crystallization conditions were followed as described above except thata pipette tip employed in previously had been reused. Presumably, thecrystal showering effect was caused by small nucleation units which hadformed in the used tip and which provided sites of nucleation for thecrystals. Addition of a small amount (0.5 μl) of the drops containingthe crystal showers to a new drop under standard production growthconditions resulted in a shower of crystals overnight. This method wasused to produce several trays of drops containing crystal showers whichwe termed “seed stock”.

The number of nucleation initiation units (NIU) contained within the“seed stock” drops was estimated to attempt to improve thereproducibility and quality of the r-hu-GCSF crystals. To determine thenumber of NIU in the “seed stock”, an aliquot of the drop was seriallydiluted along a 96 well microtiter plate. The microtiter plate wasprepared by adding 50 μl of a solution containing equal volumes ofr-hu-G-CSF (33 mg/ml) and the crystal growth solution (described above)in each well. An aliquot (3 μl) of one of the “seed stock” drops wastransferred to the first well of the microtiter plate. The solution inthe well was mixed and 3 μl was then transferred to the next well alongthe row of the microtiter plate. Each row of the microtiter plate wassimilarly prepared and the tray was sealed with plastic tape. Overnight,small crystals formed in the bottom of the wells of the microtiter plateand the number of crystals in the wells were correlated to the dilutionof the original “seed stock”. To produce large single crystals, the“seed stock” drop was appropriately diluted into fresh CGS and then analiquot of this solution containing the NIU was transferred to a drop

Once crystallization conditions had been optimized, crystals were grownin a production method in which 3 ml each of CGS and r-hu-G-CSF (33mg/ml) were mixed to create five trays (each having 24 wells). Thismethod included the production of the refined crystallization solutionin liter quantities, mixing this solution with protein and placing theprotein/crystallization solution in either hanging drop or sitting droptrays. This process typically yielded 100 to 300 quality crystals (>0.5mm) in about five days.

e. Experimental Methods

Materials

Crystallographic information was obtained starting with r-hu-met-G-CSFwith the amino acid sequence as provided in FIG. 1 (Seq. ID. No. 2) witha specific activity of 1.0+/−0.6×10⁸ U/mg (as measured by cellmitogenesis assay in a 10 mM acetate buffer at pH 4.0 (in Water forInjection) at a concentration of approximately 3 mg/ml solution wasconcentrated with an Amicon concentrator at 75 psi using a YM10 filter.The solution was typically concentrated 10 fold at 4° C. and stored forseveral months.

Initial Screening

Crystals suitable for X-ray analysis were obtained by vapor-diffusionequilibrium using hanging drops. For preliminary screening, 7 μl of theprotein solution at 33 mg/ml (as prepared above) was mixed with an equalvolume of the well solution, placed on siliconized glass plates andsuspended over the well solution utilizing Linbro tissue culture plates(Flow Laboratories, McLean, Va.). All of the pipetting was performedwith the Accuflex pipetter, however, trays were removed from theautomated pipetter after the well solutions had been created andthoroughly mixed for at least ten minutes with a table top shaker. TheLinbro trays were then returned to the pipetter which added the well andprotein solutions to the siliconized cover slips. The cover slips werethen inverted and sealed over 1 ml of the well solutions with silicongrease.

The components of the automated crystallization system are as follows. APC-DOS computer system was used to design a matrix of crystallizationsolutions based on the concentration of their components. These matriceswere produced with either MRF of the Lotus™ spread sheet (describedabove). The final product of these programs is a data file. This filecontains the information required by the SUX program to pipette theappropriate volume of the stock solutions to obtain the concentrationsdescribed in the matrices. The SUX program information was passedthrough a serial I/O port and used to dictate to the Accuflex pipettingsystem the position of the valve relative to the stock solutions, theamount of solution to be retrieved, and then pipetted into the wells ofthe microtiter plates and the X-Y position of each well (the column/rowof each well). Additional information was transmitted to the pipetterwhich included the Z position (height) of the syringe during filling aswell as the position of a drain where the system pauses to purge thesyringe between fillings of different solutions. The 24 well microtiterplate (either Linbro or Cryschem) and cover slip holder was placed on aplate which was moved in the X-Y plane. Movement of the plate allowedthe pipetter to position the syringe to pipette into the wells. It alsopositioned the coverslips and vials and extract solutions from thesesources. Prior the pipetting, the Linbro microtiter plates had a thinfilm of grease applied around the edges of the wells. After thecrystallization solutions were prepared in the wells and before theywere transferred to the cover slips, the microtiter plate was removedfrom the pipetting system, and solutions were allowed to mix on a tabletop shaker for ten minutes. After mixing, the well solution was eithertransferred to the cover slips (in the case of the hanging dropprotocol) or transferred to the middle post in the well (in the case ofthe sitting drop protocol). Protein was extracted from a vial and addedto the coverslip drop containing the well solution (or to the post).Plastic tape was applied to the top of the Cryschem plate to seal thewells.

Production Growth

Once conditions for crystallization had been optimized, crystal growthwas performed utilizing a “production” method. The crystallizationsolution which contained 100 mM Mes pH 5.8, 380 mM MgCl2, 220 mM LiSO4,and 8% PEG 8K was made in one liter quantities. Utilizing an Eppindorfsyringe pipetter, 1 ml aliquots of this solution were pipetted into eachof the wells of the Linbro plate. A solution containing 50% of thissolution and 50% G-CSF (33 mg/ml) was mixed and pipetted onto thesiliconized cover slips. Typical volumes of these drops were between 50and 100 μl and because of the large size of these drops, great care wastaken in flipping the coverslips and suspending the drops over thewells.

Data Collection

The structure has been refined with X-PLOR (Bruniger, X-PLOR version3.0, A system for crystallography and NMR, Yale University, New Haven,Conn.) against 2.2 Å data collected on an R-AXIS (Molecular Structure,Corp. Houston, Tex.) imaging plate detector.

f. Observations

As an effective recombinant human therapeutic, t-hu-G-CSF has beenproduced in large quantities and gram levels have been made availablefor structural analysis. The crystallization methods provided herein arelikely to find other applications as other proteins of interest becomeavailable. This method can be applied to any crystallographic projectwhich has large quantities of protein (approximately >200 mg). As oneskilled in the art will recognize, the present materials and methods maybe modified and equivalent materials and methods may be available forcrystallization of other proteins.

B. Computer Program for Visualizing the Three Dimensional Structure ofG-CSF

Although diagrams, such as those in the Figures herein, are useful forvisualizing the three dimensional structure of G-CSF, a computer programwhich allows for stereoscopic-viewing of the molecule is contemplated aspreferred. This stereoscopic viewing, or “virtual reality” as those inthe art sometimes refer to it, allows one to visualize the structure inits three dimensional form from every angle in a wide range ofresolution, from macromolecular structure down to the atomic level. Thecomputer programs contemplated herein also allow one to changeperspective of the viewing angle of the molecule, for example byrotating the molecule. The contemplated programs also respond to changesso that one may, for example, delete, add, or substitute one or moreimages of atoms, including entire amino acid residues, or add chemicalmoieties to existing or substituted groups, and visualize the change instructure.

Other computer based systems may be used; the elements being: (a) ameans for entering information such as orthogonal coordinates or othernumerically assigned coordinates of the three dimensional structure ofG-CSF; (b) a means for expressing such coordinates, such as visual meansso that one may view the three dimensional structure and correlate suchthree dimensional structure with the composition of the G-CSF molecule,such as the amino acid composition; and (c) optionally, means forentering information which alters the composition of the G-CSF moleculeexpressed, so that the image of such three dimensional structuredisplays the altered composition.

The coordinates for the preferred computer program used are presented inFIG. 5. The preferred computer program is Insight II, version 4,available from Biosym in San Diego, Calif. For the raw crystallographicstructure, the observed intensities of the diffraction data (“F-obs”)and the orthogonal coordinates are also deposited in the Protein DataBank, Chemistry Department, Brookhaven National Laboratory, Upton, N.Y.19723, USA and these are herein incorporated by reference.

Once the coordinates are entered into the Insight II program, one caneasily display the three dimensional G-CSF molecule representation on acomputer screen. The preferred computer-system for display is SiliconGraphics 320 VGX (San Diego, Calif.). For stereoscopic viewing, one maywear eyewear (Crystal Eyes, Silicon Graphics) which allows one tovisualize the G-CSF molecule in three dimensions stereoscopically, soone may turn the molecule and envision molecular design.

Thus, the present invention provides a method of designing or preparinga G-CSF analog with the aid of a computer comprising:

-   -   (a) providing said computer with the means for displaying the        three dimensional structure of a G-CSF molecule including        displaying the composition of moieties of said G-CSF molecule,        preferably displaying the three dimensional location of each        amino acid, and more preferably displaying the three dimensional        location of each atom of a G-CSF molecule;    -   (b) viewing said display;    -   (c) selecting a site on said display for alteration in the        composition of said molecule or the location of a moiety; and    -   (d) preparing a G-CSF analog with such alteration.

The alteration may be selected based on the desired structuralcharacteristics of the end-product G-CSF analog, and considerations forsuch design are described in more detail below. Such considerationsinclude the location and compositions of hydrophobic amino acidresidues, particularly residues internal to the helical structures of aG-CSF molecule which residues, when altered, alter the overall structureof the internal core of the molecule and may prevent receptor binding;the location and compositions of external loop structures, alteration ofwhich may not affect the overall structure of the G-CSF molecule.

FIGS. 2-4 illustrate the overall three dimensional conformation indifferent ways. The topological diagram, the ribbon diagram, and thebarrel diagram all illustrate aspects of the conformation of G-CSF.

FIG. 2 illustrates a comparison between G-CSF and other molecules. Thereis a similarity of architecture, although these growth factors differ inthe local conformations of their loops and bundle geometrics. Theup-up-down-down topology with two long crossover connections isconserved, however, among all six of these molecules, despite thedissimilarity in amino acid sequence.

FIG. 3 illustrates in more detail the secondary structure of recombinanthuman G-CSF. This ribbon diagram illustrates the handedness of thehelices and their positions relative to each other.

FIG. 4 illustrates in a different way the conformation of recombinanthuman G-CSF. This “barrel” diagram illustrates the overall architectureof recombinant human G-CSF.

C. Preparation of Analogs Using M13 Mutagenesis

This example relates to the preparation of G-CSF analogs using sitedirected mutagenesis techniques involving the single strandedbacteriophage M13, according to methods published in PCT Application No.WO 85/00817 (Souza et al., published Feb. 28, 1985, herein incorporatedby reference). This method essentially involves using a single-strandednucleic acid template of the non-mutagenized sequence, and binding to ita smaller oligonucleotide containing the desired change in the sequence.Hybridization conditions allow for non-identical sequences to hybridizeand the remaining sequence is filled in to be identical to the originaltemplate. What results is a double stranded molecule, with one of thetwo strands containing the desired change. This mutagenized singlestrand is separated, and used itself as a template for its complementarystrand. This creates a double stranded molecule with the desired change.

The original G-CSF nucleic acid sequence used is presented in FIG. 1(Seq. ID. No. 1), and the oligonucleotides containing the mutagenizednucleic acid(s) are presented in Table 2. Abbreviations used herein foramino acid residues and nucleotides are conventional, see Stryer,Biochemistry, 3d Ed., W.H. Freeman and Company, New York, N.Y. 1988,inside back cover.

The original G-CSF nucleic acid sequence was first placed into vectorM13mp21. The DNA from single stranded phage M13mp21 containing theoriginal G-CSF sequence was then isolated, and resuspended in water. Foreach reaction, 200 ng of this DNA was mixed with a 1.5 pmole ofphosphorylated oligonucleotide (Table 2) and suspended in 0.1M Tris,0.01M MgCl₂, 0.005M DTT, 0.1 mM ATP, pH 8.0. The DNAs were annealed byheating to 65° C. and slowly cooling to room temperature.

Once cooled, 0.5 mM of each ATP, DATP, dCTP, dGTP, TTP, one unit of T4DNA ligase and one unit of Klenow fragment of E. coli polymerase 1 wereadded to the one unit of annealed DNA in 0.1M Tris, 0.025M NaCl, 0.01MMgCl₂, 0.01M DTT, pH 7.5.

The now double stranded, closed circular DNA was used to transfect E.coli without further purification. Plaques were screened by lifting theplaques with nitrocellulose filters, and then hybridizing the filterswith single stranded DNA end-labeled with P³² for one hour at 55-60°.After hybridization, the filters were washed at 0-3° C. below the melttemperature of the oligo (2° C. for A-T, 4° C. for G-C) whichselectively left autoradiography signals corresponding to plaques withphage containing the mutated sequence. Positive clones were confirmed bysequencing.

Set forth below are the oligonucleotides used for each G-CSF analogprepared via the M13 mutagenesis method. The nomenclature indicates theresidue and the position of the original amino acid (i.e., lysine atposition 17), and the residue and position of the substituted amino acid(i.e., arginine 17). A substitution involving more than one residue isindicated via superscript notation, with commas between the notedpositions or a semicolon indicating different residues. Deletions withno substitutions are so noted. The oligonucleotide sequences used forM13-based mutagenesis are next indicated; these oligonucleotides weremanufactured synthetically, although the method of preparation is notcritical, any nucleic acid synthesis method and/or equipment may beused. The length of the oligo is also indicated. As indicated above,these oligos were allowed to contact the single stranded phage vector,and then single nucleotides were added to complete the G-CSF analognucleic acid sequence.

TABLE 2 Length G-CSF ANALOGS SEQUENCES (5′ -> 3′) (nucleotide) Seg. ID.Nos. Lys¹⁷ -> Arg¹⁷ CTT TCT GCT GCG TTG TCT GGA ACA 24 Seq. ID. No. 3Lys²⁴ -> Arg²⁴ ACA GGT TCG TCG TAT CCA GGG TG 23 Seq. ID. No. 4 Lys³⁵ ->Arg³⁵ CAC TGC AAG AAC GTC TGT GCG CT 23 Seq. ID. No. 5 Lys⁴¹ -> Arg⁴¹CGC TAC TTA CCG TCT GTG CCA TC 23 Seq. ID. No. 6 Lys^(17, 24, 35) -> CTTTCT GCT GCG TTG TCT GGA ACA 24 Seq. ID. No. 7 Arg^(17, 24, 35) ACA GGTTCG TCG TAT CCA GGG TG 23 Seq. ID. No. 8 CAC TGC AAG AAC GTC TGT GCG CT23 Seq. ID. No. 9 Lys^(17, 24, 41) -> CTT TCT GCT GCG TTG TCT GGA ACA 24Seq. ID. No. 10 Arg^(17, 24, 41) ACA GGT TCG TCG TAT CCA GGG TG 23 Seq.ID. No. 11 CGC TAG TTA CCG TCT GTC CCA TC 23 Seq. ID. No. 12Lys^(17, 35, 41) -> CTT TCT GCT GCG TTG TCT GGA ACA 24 Seq. ID. No. 13Arg^(17, 35, 41) CAC TGC AAG AAC GTC TGT GCG CT 23 Seq. ID. No. 14 CGCTAC TTA CCG TCT GTG CCA TC 23 Seq. ID. No. 15 Lys^(24, 35, 41) -> ACAGGT TCG TCG TAT CCA GGG TG 23 Seq. ID. No. 16 Arg^(24, 35, 41) CAC TGCAAG AAC GTC TGT GCG CT 23 Seq. ID. No. 17 CGC TAC TTA CCG TCT GTG CCA TC23 Seq. ID. No. 18 Lys^(17, 24, 35, 41) -> CTT TCT GCT GCG TTG TCT GGAACA 24 Seq. ID. No. 19 Arg^(17, 24, 35, 41) ACA GGT TCG TCG TAT CCA GGGTG 23 Seq. ID. No. 20 CAC TGC AAG AAC GTC TGT GCG CT 23 Seq. ID. No. 21CGC TAC TTA CCG TCT GTG CCA TC 23 Seq. ID. No. 22 Cys¹⁸->Ala¹⁸ TCT GCTGAA AGC TCT GGA ACA GG 23 Seq. ID. No. 23 Gln⁶⁸ -> Glu⁶⁸ CTT GTC CAT CTGAAG CTC TTC AG 23 Seq. ID. No. 24 Cys^(37, 43) -> GAA AAA CTG TCC GCTACT TAC AAA 37 Seq. ID. No. 25 Ser^(37, 43) CTG TCC CAT CCG G Gln²⁶ ->Ala²⁶ TTC GTA AAA TCG CGG GTG ACG G 22 Seq. ID. No. 26 Gln¹⁷⁴ -> Ala¹⁷⁴TCA TCT GGC TGC GCC GTA ATA G 22 Seq. ID. No. 27 Arg¹⁷⁰ -> Ala¹⁷⁰ CCGTGT TCT GGC TCA TCT GGC T 22 Seq. ID. No. 28 Arg¹⁶⁷ -> Ala¹⁶⁷ GAA GTATCT TAC GCT GTT CTG CGT 24 Seq. ID. No. 29 Deletion 167 GAA GTA TCT TACTAA GTT CTG CGT C 25 Seq. ID. No. 30 Lys⁴¹ -> Ala⁴¹ CGC TAC TTA CGC ACTGTG CCA T 22 Seq. ID. No. 31 His⁴⁴ -> Lys⁴⁴ CAA ACT GTG CAA GCC GGA AGAG 22 Seq. ID. No. 32 Glu⁴⁷ -> Ala⁴⁷ CAT CCG GAA GCA CTG GTA CTG C 22Seq. ID. No. 33 Arg²³ -> Ala²³ GGA ACA GGT TGC TAA AAT CCA GG 23 Seq.ID. No. 34 Lys²⁴ -> Ala²⁴ GAA CAG GTT CGT GCG ATC CAG GGT G 25 Seq. ID.No. 35 Glu²⁰ -> Ala²⁰ GAA ATG TCT GGC ACA GGT TCG T 22 Seq. ID. No. 36Asp²⁸ -> Ala²⁸ TCC AGG GTG CCG GTG CTG C 19 Seq. ID. No. 37 Met¹²⁷ ->Glu¹²⁷ AAG AGC TCG GTG AGG CAC CAG CT 23 Seq. ID. No. 38 Met¹³⁸ ->Glu¹³⁸ CTC AAG GTG CTG AGC CGG CAT TC 23 Seq. ID. No. 39 Met¹²⁷ ->Leu¹²⁷ GAG CTC GGT CTG GCA CCA GC 20 Seq. ID. No. 40 Met¹³⁸ ->Leu¹³⁸ TCAAGG TGC TCT GCC GGC ATT 21 Seq. ID. No. 41 Ser¹³ -> Ala¹³ TCT GCC GCAAGC CTT TCT GCT GA 23 Seq. ID. No. 42 Lys¹⁷ -> Ala¹⁷ CTT TCT GCT GGC ATGTCT GGA ACA 24 Seq. ID. No. 43 Gln¹²¹ -> Ala¹²¹ CTA TTT GGC AAG CGA TGGAAG AGC 24 Seq. ID. No. 44 Glu¹²⁴ -> Ala²⁴ CAG ATG GAA GCG CTC GGT ATG21 Seq. ID. No. 45 Met^(127, 138) -> GAG CTC GGT CTG GCA CCA GC 20 Seq.ID. No. 46 Leu^(127, 138) TCA AGG TGC TCT GCC GGC ATT 21 Seq. ID. No. 47**Glu²⁰ -> Ala²⁰; GAA ATG TCT GGC ACA GGT TCG T 22 Seq. ID. No. 48 Ser¹³->Gly¹³ **This analog came about during the preparation of G-CSF analogGlu²⁰ -> Ala²⁰. As several clones were being sequenced to identify theGlu²⁰ -> Ala²⁰ analog, the Glu²⁰ -> Ala²⁰; Ser¹³ -> Gly¹³ analog wasidentified. This double mutant was the result of an in vitro Klenow DNApolymerase reaction mistake.

D. Preparation of G-CSF Analogs Using DNA Amplification

This example relates to methods for producing G-CSF analogs using a DNAamplification technique. Essentially, DNA encoding each analog wasamplified in two separate pieces, combined, and then the total sequenceitself amplified. Depending upon where the desired change in theoriginal G-CSF DNA was to be made, internal primers were used toincorporate the change, and generate the two separate amplified pieces.For example, for amplification of the 5′ end of the desired analog DNA,a 5′ flanking primer (complementary to a sequence of the plasmidupstream from the G-CSF original DNA) was used at one end of the regionto be amplified, and an internal primer, capable of hybridizing to theoriginal DNA but incorporating the desired change, was used for primingthe other end. The resulting amplified region stretched from the 5′flanking primer through the internal primer. The same was done for the3′ terminus, using a 3′ flanking primer (complementary to a sequence ofthe plasmid downstream from the G-CSF original DNA) and an internalprimer complementary to the region of the intended mutation. Once thetwo “halves” (which may or may not be equal in size, depending on thelocation of the internal primer) were amplified, the two “halves” wereallowed to connect. Once connected, the 5′ flanking primer and the 3′flanking primer were used to amplify the entire sequence containing thedesired change.

If more than one change is desired, the above process may be modified toincorporate the change into the internal primer, or the process may berepeated using a different internal primer. Alternatively, the geneamplification process may be used with other methods for creatingchanges in nucleic acid sequence, such as the phage based mutagenesistechnique as described above. Examples of process for preparing analogswith more than one change are described below.

To create the G-CSF analogs described below, the template DNA used wasthe sequence as in FIG. 1 plus certain flanking regions (from a plasmidcontaining the G-CSF coding region). These flanking regions were used asthe 5′ and 3′ flanking primers and are set forth below. Theamplification reactions were performed in 40 μl volumes containing 10 mMTris-HCl, 1.5 mM MgCl₂, 50 mM KCl, 0.1 mg/ml gelatin, pH 8.3 at 20° C.The 40 μl reactions also contained 0.1 mM of each dNTP, 10 pmoles ofeach primer, and 1 ng of template DNA. Each amplification was repeatedfor 15 cycles. Each cycle consisted of 0.5 minutes at 94° C., 0.5minutes at 50° C., and 0.75 minutes at 72° C. Flanking primers were 20nucleotides in length and internal primers were 20 to 25 nucleotides inlength. This resulted in multiple copies of double stranded DNA encodingeither the front portion or the back portion of the desired G-CSFanalog.

For combining the two “halves”, 1/40 of each of the two reactions wascombined in a third DNA amplification reaction. The two portions wereallowed to anneal at the internal primer location, as their ends bearingthe mutation were complementary, and following a cycle ofpolymerization, give rise to a full length DNA sequence. Once soannealed, the whole analog was amplified using the 5′ and 3′ flankingprimers. This amplification process was repeated for 15 cycles asdescribed above.

The completed, amplified analog DNA sequence was cleaved with XbaI andXhoI restriction endonuclease to produce cohesive ends for insertioninto a vector. The cleaved DNA was placed into a plasmid vector, andthat vector was used to transform E. coli. Transformants were challengedwith kanamycin at 50 ug/ml and incubated at 30° C. Production of G-CSFanalog protein was confirmed by polyacrylamide gel electrophoresis of awhole cell lysate. The presence of the desired mutation was confirmed byDNA sequence analysis of plasmid purified from the production isolate.Cultures were then grown, and cells were harvested, and the G-CSFanalogs were purified as set forth below.

Set forth below in Table 3 are the specific primers used for each analogmade using gene amplification.

TABLE 3 Analog Internal Primer (5′ -> 3′) SEQ. ID. NO. His⁴⁴ -> Ala⁴⁴ 5′primer-TTCCGGAGCGCACAGTTTG Seq. ID. No. 49 3′primer-CAAACTGTGGGCTCCGGAAGAGC Seq. ID. No. 50 Thr¹¹⁷ -> Ala¹¹⁷ 5′primer-ATGCCAAATTGCAGTAGCAAAG Seq. ID. No. 51 3′primer-CTTTGCTACTGCAATTTGGCAACA Seq. ID. No. 52 Asp¹¹⁰ -> Ala¹¹⁰ 5′primer-ATCAGCTACTGCTAGCTGCAGA Seq. ID. No. 53 3′primer-TCTGCAGCTAGCAGTAGCTGACT Seq. ID. No. 54 Gln²¹ -> Ala²¹ 5′primer-TTACGAACCGCTTCCAGACATT Seq. ID. No. 55 3′primer-AATGTCTGGAAGCGGTTCGTAAAAT Seq. ID. No. 56 Asp¹¹³ -> Ala¹¹³ 5′primer-GTAGCAAATGCAGCTACATCTA Seq. ID. No. 57 3′primer-TAGATGTAGCTGCATTTGCTACTAC Seq. ID. No. 58 His⁵³ -> Ala⁵³ 5′primer-CCAAGAGAAGCACCCAGCAG Seq. ID. No. 59 3′primer-CTGCTGGGTGCTTCTCTTGGGA Seq. ID. No. 60

For each analog, the following 5′ flanking primer was used:

5′-CACTGGCGGTGATAATGAGC (Seq. ID. No. 61)

For each analog, the following 3′ flanking primer was used:

3′-GGTCATTACGGACCGGATC (Seq. ID. No. 62)

1. Construction of Double Mutation

To make G-CSF analog Gln^(12,21)->Glu^(12,21), two separate DNAamplifications were conducted to create the two DNA mutations. Thetemplate DNA used was the sequence as in FIG. 1 (Seq.ID. No.1) pluscertain flanking regions (from a plasmid containing the G-CSF codingregion). The precise sequences are listed below. Each of the two DNAamplification reactions were carried out using a Perkin Elmer/Cetus DNAThermal Cycler. The 40 μl reaction mix consisted of 1×PCR Buffer(Cetus), 0.2 mM each of the 4 dXTPs (Cetus), 50 pmoles of each primeroligonucleotide, 2 ng of G-CSF template DNA (on a plasmid vector), and 1unit of Taq polymerase (Cetus). The amplification process was carriedout for 30 cycles. Each cycle consisted of 1 minute at 94° C., 2 minutesat 50° C., and 3 minutes at 72° C.

DNA amplification “A” used the oligonucleotides:

(Seq. ID. No. 63) 5′ CCACTGGCGGTGATACTGAGC 3′ and (Seq. ID. No. 64) 5′AGCAGAAAGCTTTCCGGCAGAGAAGAAGCAGGA 3′

DNA amplification “B” used the oligonucleotides:

5′ GCCGCAAAGCTTTCTGCTGAAATGTCTGGAAGAGGTTCGTAAAATCCAGGGTGA 3′ (Seq. ID.No. 65) and 5′ CTGGAATGCAGAAGCAAATGCCGGCATAGCACCTTCAGTCGGTTGCAGAGTGGTCCA3′ (Seq. ID. No. 66)

From the 109 base pair double stranded DNA product-obtained after DNAamplification “A”, a 64 base pair XbaI to HindIII DNA fragment was cutand isolated that contained the DNA mutation Gln¹²->Glu¹². From the 509base pair double stranded DNA product obtained after DNA amplification“B”, a 197 base pair HindIII to BsmI DNA fragment was cut and isolatedthat contained the DNA mutation Gln²¹->Glu²¹.

The “A” and “B” fragments were ligated together with a 4.8 kilo-basepair XbaI to BsmI DNA plasmid vector fragment. The ligation mixconsisted of equal molar DNA restriction fragments, ligation buffer (25mM Tris-HCl pH 7.8, 10 mM MgCl₂, 2 mM DTT, 0.5 mM rATP, and 100 μg/mlBSA) and T4 DNA liqase and was incubated overnight at 14° C. The ligatedDNA was then transformed into E. coli FM5 cells by electroporation usinga Bio Rad Gene Pulsar apparatus (BioRad, Richmond, Calif.). A clone wasisolated and the plasmid construct verified to contain the two mutationsby DNA sequencing. This “intermediate” vector also contained a deletionof a 193 base pair BsmI to BsmI DNA fragment. The final plasmid vectorwas constructed by ligation and transformation (as described above) ofDNA fragments obtained by cutting and isolating a 2 kilo-base pair SstIto BamHI DNA fragment from the intermediate vector, a 2.8 kbp SstI toEcoRI DNA fragment from the plasmid vector, and a 360 bp BamHI to EcoRIDNA fragment from the plasmid vector. The final construct was verifiedby DNA sequencing the G-CSF gene. Cultures were grown, and the cellswere harvested, and the G-CSF analogs were purified as set forth below.

As indicated above, any combination of mutagenesis techniques may beused to generate a G-CSF analog nucleic acid (and expression product)having one or more than one alteration. The two examples above, usingM13-based mutagenesis and gene amplification-based mutagenesis, areillustrative.

E. Expression of G-CSF Analog DNA

The G-CSF analog DNAs were then placed into a plasmid vector and used totransform E. coli strain FM5 (ATCC#53911). The present G-CSF analog DNAscontained on plasmids and in bacterial host cells are available from theAmerican Type Culture Collection, Rockville, Md., and the accessiondesignations are indicated below.

One liter cultures were grown in broth containing 10 g tryptone, 5 gyeast extract and 5 g NaCl) at 30° C. until reaching a density at A⁶⁰⁰of 0.5, at which point they were rapidly heated to 42° C. The flaskswere allowed to continue shaking at for three hours.

Other prokaryotic or eukaryotic host cells may also be used, such asother bacterial cells, strains or species, mammalian cells in culture(COS, CHO or other types) insect cells or multicellular organs ororganisms, or plant cells or multicellular organs or organisms, and askilled practitioner will recognize the appropriate host. The presentG-CSF analogs and related compositions may also be preparedsynthetically, as, for example, by solid phase peptide synthesismethods, or other chemical manufacturing techniques. Other cloning andexpression systems will be apparent to those skilled in the art.

F. Purification of G-CSF Analog Protein

Cells were harvested by centrifugation (10,000×G, 20 minutes, 4° C.).The pellet (usually 5 grams) was resuspended in 30 ml of 1 mM DTT andpassed three times through a French press cell at 10,000 psi. The brokencell suspension was centrifuged at 10,000 g for 30 minutes, thesupernatant removed, and the pellet resuspended in 30-40 ml water. Thiswas recentrifuged at 10,000×G for 30 minutes, and this pellet wasdissolved in 25 ml of 2% Sarkosyl and 50 mM Tris at pH 8. Copper sulfatewas added to a concentration of 40 μM, and the mixture was allowed tostir for at least 15 hours at 15-25° C. The mixture was then centrifugedat 20,000×G for 30 minutes. The resultant solubilized protein mixturewas diluted four-fold with 13.3 mM Tris, pH 7.7, after which was addedapproximately 20 g Dowex™ (BioRad, Richmond, Calif.) equilibrated in 20mM Tris, pH 7.7. The mixture was stirred 90 minutes at room temperatureand then the Dowex™ was filtered out. The supernatant was then appliedto a DEAE-cellulose (Whatman DE-52) column equilibrated in 20 mM Tris,pH 7.7. After loading and washing the column with the same buffer, theanalogs were eluted with 20 mM Tris/NaCl (between 35 mM to 100 mMdepending on the analog, as indicated below), pH 7.7. For most of theanalogs, the eluent from the DEAE column was adjusted to a pH of 5.4,with 50% acetic acid and diluted as necessary (to obtain the properconductivity) with 5 mM sodium acetate pH 5.4. The solution was thenloaded onto a CM-sepharose column equilibrated in 20 mM sodium acetate,pH 5.4. The column was then washed with 20 mM NaAc, pH 5.4 until theabsorbance at 280 nm was approximately zero. The G-CSF analog was theneluted with sodium acetate/NaCl in concentrations as described below inTable 4. The DEAE column eluents for those analogs not applied to theCM-sepharose column were dialyzed directly into 10 mM NaAc, ph 4.0buffer. The purified G-CSF analogs were then suitably isolated for invitro analysis. The salt concentrations used for eluting the analogsvaried, as noted above. Below, the salt concentrations for the DEAEcellulose column and for the CM-sepharose column are listed:

TABLE 4 Salt Concentrations DEAE CM- SEQ. ID. Analog Cellulose SepharoseNOS. Lys¹⁷->Arg¹⁷ 35 mM 37.5 mM   Seq. ID. No. 67 Lys²⁴->Arg²⁴ 35 mM37.5 mM   Seq. ID. No. 68 Lys³⁵->Arg³⁵ 35 mM 37.5 mM   Seq. ID. No. 69Lys⁴¹->Arg⁴¹ 35 mM 37.5 mM   Seq. ID. No. 70Lys^(17,24,35)->Arg^(17,24,35) 35 mM 37.5 mM   Seq. ID. No. 71Lys^(17,35,41)->Arg^(17,35,41) 35 mM 37.5 mM   Seq. ID. No. 72Lys^(24,35,41)->Arg^(24,35,41) 35 mM 37.5 mM   Seq. ID. No. 73Lys^(17,24,35,41) -> 35 mM 37.5 mM   Seq. ID. No. 74 Arg^(17,24,35,41)Lys^(17,24,41)->Arg^(17,24,41) 35 mM 37.5 mM   Seq. ID. No. 75Gln⁶⁸->Glu⁶⁸ 60 mM 37.5 mM   Seq. ID. No. 76 Cys^(37,43)->Ser^(37,43) 40mM 37.5 mM   Seq. ID. No. 77 Gln²⁶->Ala²⁶ 40 mM 40 mM Seq. ID. No. 78Gln¹⁷⁴->Ala¹⁷⁴ 40 mM 40 mM Seq. ID. No. 79 Arg¹⁷⁰->Ala¹⁷⁰ 40 mM 40 mMSeq. ID. No. 80 Arg¹⁶⁷->Ala¹⁶⁷ 40 mM 40 mM Seq. ID. No. 81 Deletion 167*N/A N/A Seq. ID. No. 82 Lys⁴¹->Ala⁴¹ 160 mM  40 mM Seq. ID. No. 83His⁴⁴->Lys⁴⁴ 40 mM 60 mM Seq. ID. No. 84 Glu⁴⁷->Ala⁴⁷ 40 mM 40 mM Seq.ID. No. 85 Arg²³->Ala²³ 40 mM 40 mM Seq. ID. No. 86 Lys²⁴->Ala²⁴ 120 mM 40 mM Seq. ID. No. 87 Glu²⁰->Ala²⁰ 40 mM 60 mM Seq. ID. No. 88Asp²⁸->Ala²⁸ 40 mM 80 mM Seq. ID. No. 89 Met¹²⁷->Glu¹²⁷ 80 mM 40 mM Seq.ID. No. 90 Met¹³⁸->Glu¹³⁸ 80 mM 40 mM Seq. ID. No. 91 Met¹²⁷->Leu¹²⁷ 40mM 40 mM Seq. ID. No. 92 Met¹³⁸->Leu¹³⁸ 40 mM 40 mM Seq. ID. No. 93Cys¹⁸->Ala¹⁸ 40 mM 37.5 mM   Seq. ID. No. 94 Gln^(12,21)->Glu^(12,21) 60mM 37.5 mM   Seq. ID. No. 95 Gln^(12,21,68)->Glu^(12,21,68) 60 mM 37.5mM   Seq. ID. No. 96 Glu²⁰->Ala²⁰; 40 mM 80 mM Seq. ID. No. 97Ser¹³->Gly¹³ Met^(127,138)->Leu^(127,138) 40 mM 40 mM Seq. ID. No. 98Ser¹³->Ala¹³ 40 mM 40 mM Seq. ID. No. 99 Lys¹⁷->Ala¹⁷ 80 mM 40 mM Seq.ID. No. 100 Gln¹²¹->Ala¹²¹ 40 mM 60 mM Seq. ID. No. 101 Gln²¹->Ala²¹ 50mM Gradient Seq. ID. No. 102 0-150 mM   His⁴⁴->Ala⁴⁴** 40 mM N/A Seq.ID. No. 103 His⁵³->Ala⁵³** 50 mM N/A Seq. ID. No. 104 Asp¹¹⁰->Ala¹¹⁰**40 mM N/A Seq. ID. No. 105 Asp¹¹³->Ala¹¹³** 40 mM N/A Seq. ID. No. 106Thr¹¹⁷->Ala¹¹⁷** 50 mM N/A Seq. ID. No. 107 Asp²⁸->Ala²⁸; 50 mM N/A Seq.ID. No. 108 Asp¹¹⁰->Ala¹¹⁰** Glu¹²⁴->Ala¹²⁴** 40 mM 40 mM Seq. ID. No.109 *For Deletion 167, the data are unavailable. **For these analogs,the DEAE cellulose column alone was use for purification.

The above purification methods are illustrative, and a skilledpractitioner will recognize that other means are available for obtainingthe present G-CSF analogs.

G. Biological Assays

Regardless of which methods were used to create the present G-CSFanalogs, the analogs were subject to assays for biological activity.Tritiated thymidine assays were conducted to ascertain the degree ofcell division. Other biological assays, however, may be used toascertain the desired activity. Biological assays such as assaying forthe ability to induce terminal differentiation in mouse WEHI-3B (D+)leukemic cell line, also provides indication of G-CSF activity. SeeNicola, et al. Blood 54: 614-27 (1979). Other in vitro assays may beused to ascertain biological activity. See Nicola, Ann. Rev. Biochem.58: 45-77 (1989). In general, the test for biological activity shouldprovide analysis for the desired result, such as increase or decrease inbiological activity (as compared to non-altered G-CSF), differentbiological activity (as compared to non-altered G-CSF), receptoraffinity analysis, or serum half-life analysis. The list is incomplete,and those skilled in the art will recognize other assays useful fortesting for the desired end result.

The ³H-thymidine assay was performed using standard methods. Bone marrowwas obtained from sacrificed female Balb C mice. Bone marrow cells werebriefly suspended, centrifuged, and resuspended in a growth medium. A160 μl aliquot containing approximately 10,000 cells was placed intoeach well of a 96 well micro-titer plate. Samples of the purified G-CSFanalog (as prepared above) were added to each well, and incubated for 68hours. Tritiated thymidine was added to the wells and allowed toincubate for five additional hours. After the five hour incubation time,the cells were harvested, filtered, and thoroughly rinsed. The filterswere added to a vial containing scintillation fluid. The beta emissionswere counted (LKB Betaplate scintillation counter). Standards andanalogs were analyzed in triplicate, and samples which fellsubstantially above or below the standard curve were re-assayed with theproper dilution. The results reported here are the average of thetriplicate analog data relative to the unaltered recombinant human G-CSFstandard results.

H. HPLC Analysis

High pressure liquid chromatography was performed on purified samples ofanalog. Although peak position on a reverse phase HPLC column is not adefinitive indication of structural similarity between two proteins,analogs which have similar retention times may have the same type ofhydrophobic interactions with the HPLC column as the non-alteredmolecule. This is one indication of an overall similar structure.

Samples of the analog and the non-altered recombinant human G-CSF wereanalyzed on a reverse phase (0.46×25 cm) Vydac 214TP54 column(Separations Group, Inc. Hesperia, Calif.). The purified analog G-CSFsamples were prepared in 20 mM acetate and 40 mM NaCl solution bufferedat pH 5.2 to a final concentration of 0.1 mg/ml to 5 mg/ml, depending onhow the analog performed in the column. Varying amounts (depending onthe concentration) were loaded onto the HPLC column, which had beenequilibrated with an aqueous solution containing 1% isopropanol, 52.8%acetonitrile, and 38% trifluoro acetate (TFA). The samples weresubjected to a gradient of 0.86%/minute acetonitrile, and 0.002% TFA.

I. Results

Presented below are the results of the above biological assays and HPLCanalysis. Biological activity is the average of triplicate data andreported as a percentage of the control standard (non-altered G-CSF).Relative HPLC peak position is the position of the analog G-CSF relativeto the control standard (non-altered G-CSF) peak. The “+” or “−” symbolsindicate whether the analog HPLC peak was in advance of or followed thecontrol standard peak (in minutes). Not all of the variants had beenanalyzed for relative HPLC peak, and only those so analyzed are includedbelow. Also presented are the American Type Culture Collectiondesignations for E. coli host cells containing the nucleic acids codingfor the present analogs, as prepared above.

TABLE 5 Relative % Normal HPLC G-CSF SEQ. ID. Variant Analog Peak ATCCNo. Activity NOS. 1 Lys¹⁷->Arg¹⁷ N/A 69184 N/A 67 2 Lys²⁴->Arg²⁴ N/A69185 N/A 68 3 Lys³⁵->Arg³⁵ N/A 69186 N/A 69 4 Lys⁴¹->Arg⁴¹ N/A 69187N/A 70 5 Lys^(17,24,35-)>Arg^(17,24,35) N/A 69189 N/A 71 6Lys^(17,35,41-)>Arg^(17,35,41) N/A 69192 N/A 72 7Lys^(24,35,41-)>Arg^(24,35,41) N/A 69191 N/A 73 8Lys^(17,24,35,41-)>Arg^(17,24,35,41) N/A 69193 N/A 74 9Lys^(17,24,41-)>Arg^(17,24,41) N/A 69190 N/A 75 10 Gln⁶⁸->Glu⁶⁸ N/A69196 N/A 76 11 Cys^(37,43)->Ser^(37,43) N/A 69197 N/A 77 12Gln²⁶->Ala²⁶ +.96 69201   51% 78 13 Gln¹⁷⁴->Ala¹⁷⁴ +.14 69202  100% 7914 Arg¹⁷⁰->Ala¹⁷⁰ +.78 69203  100% 80 15 Arg¹⁶⁷->Ala¹⁶⁷ +.54 69204  110%81 16 Deletion¹⁶⁷ −.99 69207 N/A 82 17 Lys⁴¹->Ala⁴¹ +.25 69208   81% 8318 His⁴⁴->Lys⁴⁴ −1.53 69212   70% 84 19 Glu⁴⁷->Ala⁴⁷ +.14 69205   0% 8520 Arg²³->Ala²³ −.03 69206   31% 86 21 Lys²⁴->Ala²⁴ +1.95 69213   0% 8722 Glu²⁰->Ala²⁰ −0.07 69211   0% 88 23 Asp²⁸->Ala²⁸ −.30 69210  147% 8924 Met¹²⁷->Glu¹²⁷ N/A 69223 N/A 90 25 Met¹³⁸->Glu¹³⁸ N/A 69222 N/A 91 26Met¹²⁷->Leu¹²⁷ N/A 69198 N/A 92 27 Met¹³⁸->Leu¹³⁸ N/A 69199 N/A 93 28Cys¹⁸->Ala¹⁸ N/A 69188 N/A 94 29 Gln^(12,21)->Glu^(12,21) N/A 69194 N/A95 30 Gln^(12,21,68)->Glu^(12,21,68) N/A 69195 N/A 96 31 Glu²⁰->Ala²⁰;Ser¹³->Gly¹³ +1.74 69209   0% 97 32 Met^(127,138)->Leu^(127,138) +1.4369200   98% 98 33 Ser¹³->Ala¹³ 0 69221  110% 99 34 Lys¹⁷->Ala¹⁷ +.5069226   70% 100 35 Gln¹²¹->Ala¹²¹ +2.7 69225  100% 101 36 Gln²¹->Ala²¹+0.63 69217  9.6% 102 37 His⁴⁴->Ala⁴⁴ +1.52 69215 10.8% 103 38His⁵³->Ala⁵³ +0.99 69219  8.3% 104 39 Asp¹¹⁰->Ala¹¹⁰ +1.97 69216   29%105 40 Asp¹¹³->Ala¹¹³ −0.34 69218   0% 106 41 Thr¹¹⁷->Ala¹¹⁷ +0.4 69214 9.7% 107 42 Asp²⁸⁻>Ala²⁸; Asp¹¹⁰ Ala¹¹⁰ +3.2 69220 20.6% 108 43Glu¹²⁴->Ala¹²⁴ +0.16 69224   75% 109 44 Phe¹¹⁴->Val¹¹⁴, Thr¹¹⁷-> +0.53  0% 110 Ala¹¹⁷** **This analog was apparently a result of aninadvertent error in the oligo which was used to prepare number 41,above (Thr¹¹⁷->Ala¹¹⁷), and thus was prepared identically to the processused for that analog. “N/A” indicates data which are not available.

1. Identification of Structure-Function Relationships

The first step used to design the present analogs was to determine whatmoieties are necessary for structural integrity of the G-CSF molecule.This was done at the amino acid residue level, although the atomic levelis also available for analysis. Modification of the residues necessaryfor structural integrity results in change in the overall structure ofthe G-CSF molecule. This may or may not be desirable, depending on theanalog one wishes to produce. The working examples here were designed tomaintain the overall structural integrity of the G-CSF molecule, for thepurpose of maintain G-CSF receptor binding of the analog to the G-CSFreceptor (as used in this section below, the “G-CSF receptor” refers tothe natural G-CSF receptor, found on hematopoietic cells). It wasassumed, and confirmed by the studies presented here, that G-CSFreceptor binding is a necessary step for at least one biologicalactivity, as determined by the above biological assays.

As can be seen from the figures, G-CSF (here, recombinant humanmet-G-CSF) is an antiparallel 4-alpha helical bundle with a left-handedtwist, and with overall dimensions of 45 Å×30 Å×24 Å. The four heliceswithin the bundle are referred to as helices A, B, C and D, and theirconnecting loops are known as the AB, BC and CD loops. The helixcrossing angles range from −167.5° to −159.4°. Helices A, B, and C arestraight, whereas helix D contains two kinds of structuralcharacteristics, at Gly¹⁵⁰ and Ser¹⁶⁰ (of the recombinant humanmet-G-CSF). Overall, the G-CSF molecule is a bundle of four helices,connected in series by external loops. This structural information wasthen correlated with known functional information. It was known thatresidues (including methionine at position 1) 47, 23, 24, 20, 21, 44,53, 113, 110, 28 and 114 may be modified, and the effect on biologicalactivity would be substantial.

The majority of single mutations which lowered biological activity werecentered around two regions of G-CSF that are separated by 30 Å, and arelocated on different faces of the four helix bundle. One region involvesinteractions between the A helix and the D helix. This is furtherconfirmed by the presence of salt bridges in the non-altered molecule asfollows:

Atom Helix Atom Helix Distance Arg¹⁷⁰ N1 D Tyr¹⁶⁶ OH A 3.3 Tyr¹⁶⁶ OH DArg²³ N2 A 3.3 Glu¹⁶³ OE1 D Arg²³ N1 A 2.8 Arg²³ N1 A Gln²⁶ OE1 A 3.1Gln¹⁵⁹ NE2 D Gln²⁶ O A 3.3

Distances reported here were for molecule A, as indicated in FIG. 5(wherein three G-CSF molecules crystallized together and were designatedas A, B, and C). As can be seen, there is a web of salt bridges betweenhelix A and helix D, which act to stabilize the helix A structure, andtherefore affect the overall structure of the G-CSF molecule.

The area centering around residues Glu²⁰, Arg²³ and Lys²⁴ are found onthe hydrophilic face of the A helix (residues 20-37). Substitution ofthe residues with the non-charged alanine residue at positions 20 and 23resulted in similar HPLC retention times, indicating similarity instructure. Alteration of these sites altered the biological activity (asindicated by the present assays). Substitution at Lys²⁴ alteredbiological activity, but did not result in a similar HPLC retention timeas the other two alterations.

The second site at which alteration lowered biological activity involvesthe AB helix. Changing glutamine at position 47 to alanine (analog no.19, above) reduced biological activity (in the thymidine uptake assay)to zero. The AB helix is predominantly hydrophobic, except at the aminoand carboxy termini; it contains one turn of a 3¹⁰ helix. There are twohistadines at each termini (His⁴⁴ and His⁵⁶) and an additional glutamateat residue 46 which has the potential to form a salt bridge to His⁴⁴.The fourier transformed infra red spectrographic analysis (FTIR) of theanalog suggests this analog is structurally similar to the non-alteredrecombinant G-CSF molecule. Further testing showed that this analogwould not crystallize under the same conditions as the non-alteredrecombinant molecule.

Alterations at the carboxy terminus (Gln¹⁷⁴, Arg¹⁶⁷, and Arg¹⁷⁰) hadlittle effect on biological activity. In contrast, deletion of the lasteight residues (167-175) lowered biological activity. These results mayindicate that the deletion destabilizes the overall structure whichprevents the mutant from proper binding to the G-CSF receptor (and thusinitiating signal transduction).

Generally, for the G-CSF internal core—the internal four helix bundlelacking the external loops—the hydrophobic internal residues areessential for structural integrity. For example, in helix A, theinternal hydrophobic residues are (with methionine being position 1)Phe¹⁴, Cys¹⁸, Val²², Ile²⁵, Ile³² and Leu³⁶. Generally, for the G-CSFinternal core—the internal four helix bundle lacking the externalloops—the hydrophobic internal residues are essential for structuralintegrity. For example, in helix A, the internal hydrophobic residuesare (with methionine being position 1 as in FIG. 1, Seq.ID. No.2) Phe¹⁴,Cys¹⁸, Val²², Ile²⁵, Ile³² and Leu³⁶. The other hydrophobic residues(again with the met at position 1) are: helix B, Ala⁷², Leu⁷⁶, Leu⁷⁹,Leu⁸³, Tyr⁸⁶, Leu⁹⁰ Leu⁹³; helix C, Leu¹⁰⁴, Leu¹⁰⁷, Val¹¹¹, Ala¹¹⁴,Ile¹¹⁸, Met¹²²; and helix D, Val¹⁵⁴, Val¹⁵⁸, Phe¹⁶¹, Val¹⁶⁴, Val¹⁶⁸,Leu¹⁷².

The above biological activity data, from the presently prepared G-CSFanalogs, demonstrate that modification of the external loops interfereleast with G-CSF overall structure. Preferred loops for analogpreparation are the AB loop and the CD loop. The loops are relativelyflexible structures as compared to the helices. The loops may contributeto the proteolysis of the molecule. G-CSF is relatively fast acting invivo as the purpose the molecule serves is to generate a response to abiological challenge, i.e., selectively stimulate neutrophils. The G-CSFturnover rate is also relatively fast. The flexibility of the loops mayprovide a “handle” for proteases to attach to the molecule to inactivatethe molecule. Modification of the loops to prevent protease degradation,yet have (via retention of the overall structure of non-modified G-CSF)no loss in biological activity may be accomplished.

This phenomenon is probably not limited to the G-CSF molecule but mayalso be common to the other molecules with known similar overallstructures, as presented in FIG. 2. Alteration of the external loop of,for example hGH, Interferon β, IL-2, GM-CSF and IL-4 may provide theleast change to the overall structure. The external loops on the GM-CSFmolecule are not as flexible as those found on the G-CSF molecule, andthis may indicate a longer serum life, consistent with the broaderbiological activity of GM-CSF. Thus, the external loops of GM-CSF may bemodified by releasing the external loops from the beta-sheet structure,which may make the loops more flexible (similar to those G-CSF) andtherefore make the molecule more susceptible to protease degradation(and thus increase the turnover rate).

Alteration of these external loops may be effected by stabilizing theloops by connection to one or more of the internal helices. Connectingmeans are known to those in the art, such as the formation of a betasheet, salt bridge, disulfide bonding or hydrophobic interactions, andother means are available. Also, deletion of one or more moieties, suchas one or more amino acid residues or portions thereof, to prepare anabbreviated molecule and thus eliminate certain portions of the externalloops may be effected.

Thus, by alteration of the external loops, preferably the AB loop (aminoacids 58-72 of r-hu-met G-CSF) or the CD loop (amino acids 119 to 145 ofr-hu-met-G-CSF), and less preferably the amino terminus (amino acids1-10), one may therefore modify the biological function withoutelimination of G-CSF G-CSF receptor binding. For example, one may: (1)increase half-life (or prepare an oral dosage form, for example) of theG-CSF molecule by, for example, decreasing the ability of proteases toact on the G-CSF molecule or adding chemical modifications to the G-CSFmolecule, such as one or more polyethylene glycol molecules or entericcoatings for oral formulation which would act to change somecharacteristic of the G-CSF molecule as described above, such asincreasing serum or other half-life or decreasing antigenicity; (2)prepare a hybrid molecule, such as combining G-CSF with part or all ofanother protein such as another cytokine or another protein whicheffects signal transduction via entry through the cell through a G-CSFG-CSF receptor transport mechanism; or (3) increase the biologicalactivity as in, for example, the ability to selectively stimulateneutrophils (as compared to a non-modified G-CSF molecule). This list isnot limited to the above exemplars.

Another aspect observed from the above data is that stabilizing surfaceinteractions may affect biological activity. This is apparent fromcomparing analogs 23 and 40. Analog 23 contains a substitution of thecharged asparagine residue at position 28 for the neutrally-chargedalanine residue in that position, and such substitution resulted in a50% increase in the biological activity (as measured by the disclosedthymidine uptake assays). The asparagine residue at position 28 has asurface interaction with the asparagine residue at position 113; bothresidues being negatively charged, there is a certain amount ofinstability (due to the repelling of like charged moieties). When,however the asparagine at position 113 is replaced with theneutrally-charged alanine, the biological activity drops to zero (in thepresent assay system). This indicates that the asparagine at position113 is critical to biological activity, and elimination of theasparagine at position 28 serves to increase the effect that asparagineat position 113 possesses.

The domains required for G-CSF receptor binding were also determinedbased on the above analogs prepared and the G-CSF structure. The G-CSFreceptor binding domain is located at residues (with methionine beingposition 1) 11-57 (between the A and AB helix) and 100-118 (between theB and C helices). One may also prepare abbreviated molecules capable ofbinding to a G-CSF receptor and initiate signal transduction forselectively stimulating neutrophils by changing the external loopstructure and having the receptor binding domains remain intact.

Residues essential for biological activity and presumably G-CSF receptorbinding or signal transduction have been identified. Two distinct sitesare located on two different regions of the secondary structure. What ishere called “Site A” is located on a helix which is constrained by saltbridge contacts between two other members of the helical bundle. Thesecond site, “Site B” is located on a relatively more flexible helix,AB. The AB helix is potentially more sensitive to local pH changesbecause of the type and position of the residues at the carboxy andamino termini. The functional importance of this flexible helix may beimportant in a conformationally induced fit when binding to the G-CSFreceptor. Additionally, the extended portion of the D helix is alsoindicated to be a G-CSF receptor binding domain, as ascertained bydirect mutational and indirect comparative protein structure analysis.Deletion of the carboxy terminal end of r-hu-met-G-CSF reduces activityas it does for hGH, see, Cunningham et al. Science 244: 1081-1084(1989). Cytokines which have similar structures, such as IL-6 and GM-CSFwith predicted similar topology also center their biological activityalong the carboxy end of the D helix, see Bazan Immunology Today 11:350-354 (1990).

A comparison of the structures and the positions of G-CSF receptorbinding determinants between G-CSF and hGH suggests both molecules havesimilar means of signal transduction. Two separate G-CSF receptorbinding sites have been identified for hGH De Vos et al. Science 255:306-32 (1991). One of these binding sites (called “Site I”) is formed byresidues on the exposed faces of hGH's helix 1, the connection regionbetween helix 1 and 2, and helix 4. The second binding site (called“Site II”) is formed by surface residues of helix 1 and helix 3.

The G-CSF receptor binding determinates identified for G-CSF are locatedin the same relative positions as those identified for hGH. The G-CSFreceptor binding site located in the connecting region between helix Aand B on the AB helix (Site A) is similar in position to that reportedfor a small piece of helix (residues 38-47) of hGH. A single pointmutation in the AB helix of G-CSF significantly reduces biologicalactivity (as ascertained in the present assays), indicating the role ina G-CSF receptor-ligand interface. Binding of the G-CSF receptor maydestabilize the 3¹⁰ helical nature of this region and induce aconformation change improving the binding energy of the ligand/G-CSFreceptor complex.

In the hGH receptor complex, the first helix of the bundle donatesresidues to both of the binding sites required to dimerize the hGHreceptor. Mutational analysis of the corresponding helix of G-CSF (helixA) has identified three residues which are required for biologicalactivity. Of these three residues, Glu²⁰ and Arg²⁴ lie on one face ofthe helical bundle towards helix C, whereas the side chain of Arg²³ (intwo of the three molecules in the asymmetric unit) points to the face ofthe bundle towards helix D. The position of side chains of thesebiologically important residues indicates that similar to hGH, G-CSF mayhave a second G-CSF receptor binding site along the interface betweenhelix A and helix C. In contrast with the hGH molecule, the aminoterminus of G-CSF has a limited biological role as deletion of the first11 residues has little effect on the biological activity.

As indicated above (see FIG. 2, for example), G-CSF has a topologicalsimilarity with other cytokines. A correlation of the structure withprevious biochemical studies, mutational analysis and direct comparisonof specific residues of the hGH receptor complex indicates that G-CSFhas two receptor binding sites. Site A lies along the interface of the Aand D helices and includes residues in the small AB helix. Site B alsoincludes residues in the A helix but lies along the interface betweenhelices A and C. The conservation of structure and relative positions ofbiologically important residues between G-CSF and hGH is one indicationof a common method of signal transduction in that the receptor is boundin two places. It is therefore found that G-CSF analogs possessingaltered G-CSF receptor binding domains may be prepared by alteration ateither of the G-CSF receptor binding sites (residues 20-57 and 145-175).

Knowledge of the three dimensional structure and correlation of thecomposition of G-CSF protein makes possible a systematic, rationalmethod for preparing G-CSF analogs. The above working examples havedemonstrated that the limitations of the size and polarity of the sidechains within the core of the structure dictate how much change themolecule can tolerate before the overall structure is changed.

1. A modified G-CSF polypeptide comprising the amino acid sequence shownin SEQ ID NO: 2 and a first chemical moiety attached directly to anexternal loop; a second chemical moiety attached to the first chemicalmoiety; wherein the first chemical moiety is a polysaccharide and thesecond chemical moiety is polyethelene glycol; wherein the modifiedG-CSF polypeptide has ability to selectively stimulate the production ofneutrophils; and wherein the N terminal methionine as set forth in SEQID NO:2 is optional.
 2. The modified G-CSF polypeptide of claim 1wherein the external loop is CD loop.
 3. The modified G-CSF polypeptideof claim 1 wherein the external loop is AB loop.
 4. The modified G-CSFpolypeptide of claim 1 wherein the external loop is BC loop.